Be compatible with python-werkzeug 1.0.0.

Taken from upstream:
https://github.com/beetbox/beets/commit/d43d54e21cde97f57f19486925ab56b419254cc8

diff --git a/beetsplug/web/__init__.py b/beetsplug/web/__init__.py
index f53fb3a954..21ff5d94ed 100644
--- a/beetsplug/web/__init__.py
+++ b/beetsplug/web/__init__.py
@@ -169,7 +169,7 @@ def to_python(self, value):
         return ids
 
     def to_url(self, value):
-        return ','.join(value)
+        return ','.join(str(v) for v in value)
 
 
 class QueryConverter(PathConverter):
: <a href='/guix/'>guix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='519fe9d61f768cb5235921071f293d729413ebc5'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=519fe9d61f768cb5235921071f293d729413ebc5'>refs</a><a class='active' href='/guix/log/gnu/packages/android.scm'>log</a><a href='/guix/tree/gnu/packages/android.scm?id=519fe9d61f768cb5235921071f293d729413ebc5'>tree</a><a href='/guix/commit/gnu/packages/android.scm?id=519fe9d61f768cb5235921071f293d729413ebc5'>commit</a><a href='/guix/diff/gnu/packages/android.scm?id=519fe9d61f768cb5235921071f293d729413ebc5'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/android.scm'>
<input type='hidden' name='id' value='519fe9d61f768cb5235921071f293d729413ebc5'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=519fe9d61f768cb5235921071f293d729413ebc5'>root</a>/<a href='/guix/log/gnu?id=519fe9d61f768cb5235921071f293d729413ebc5'>gnu</a>/<a href='/guix/log/gnu/packages?id=519fe9d61f768cb5235921071f293d729413ebc5'>packages</a>/<a href='/guix/log/gnu/packages/android.scm?id=519fe9d61f768cb5235921071f293d729413ebc5'>android.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/android.scm?id=519fe9d61f768cb5235921071f293d729413ebc5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-08-03 09:10:50 +0200'>2020-08-03</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=87194d5783c1848b44a0596432cb66940d7874d2'>gnu: android: Export android-liblog.</a><span class='msg-avail'>...</span></td><td>Denis 'GNUtoo' Carikli</td></tr>
<tr><td><span title='2020-08-03 09:10:22 +0200'>2020-08-03</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=b3981bba78691799de30f38e5636259773f5d86b'>gnu: android: Export android-libcutils.</a><span class='msg-avail'>...</span></td><td>Denis 'GNUtoo' Carikli</td></tr>
<tr><td><span title='2020-07-12 23:08:15 +0200'>2020-07-12</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=b0e7b6992f3f845e83cfbca4d700b51dba50b4d5'>gnu: Remove ".git" from "https://github/…/….git".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-05-07 16:05:57 +0200'>2020-05-07</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=23a59b180b28b9fa22120c2b8305b9324442b94d'>gnu: android-libutils: Fix build failure.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-03-04 23:16:17 +0100'>2020-03-04</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=ebb7cf9e21060105d9950dd5142c0eb918083666'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-02-27 09:34:46 -0500'>2020-02-27</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=e64c5a8fe4e99eb4af24ca37574b5d4ab5a389d6'>gnu: git-repo: Really disable self update.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-02-27 09:34:46 -0500'>2020-02-27</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=0c0156089cac0b8d4d3c761ba27d3e7e8d6d3bca'>gnu: git-repo: Update to 2.4.1.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-02-24 10:54:04 -0500'>2020-02-24</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=af52ba64fa6350690d65a1aca9c89e13103fd8d0'>gnu: git-repo: Update to 2.3.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-01-15 00:24:28 +0100'>2020-01-15</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=bb93042c8beb881ab907fa802eefb3c4091039a2'>gnu: util-linux: Move libraries to separate output.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-12-02 11:32:17 +0100'>2019-12-02</span></td><td><a href='/guix/commit/gnu/packages/android.scm?id=e1b88fde12305fca3c4a739a7e8f1449f42390f1'>gnu: android-libselinux: Avoid top-level references to 'libsellinux'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>