The QuickCheck library swapped the order of the arguments of the 'cover'
function in version 2.12.  Version 0.3.4 of the Diff library still uses
the old argument order.  Swapping the argument order makes Diff work
with newer versions of QuickCheck.

See <https://github.com/commercialhaskell/stackage/issues/4289> for the
upstream bug report.

diff -ruN a/test/Test.hs b/test/Test.hs
--- a/test/Test.hs	2016-04-23 01:21:45.000000000 -0400
+++ b/test/Test.hs	2019-11-01 19:13:04.590770903 -0400
@@ -134,7 +134,7 @@
 prop_ppDiffR (DiffInput le ri) =
     let haskDiff=ppDiff $ getGroupedDiff le ri
         utilDiff= unsafePerformIO (runDiff (unlines le) (unlines ri))
-    in  cover (haskDiff == utilDiff) 90 "exact match" $
+    in  cover 90 (haskDiff == utilDiff) "exact match" $
                 classify (haskDiff == utilDiff) "exact match"
                         (div ((length haskDiff)*100) (length utilDiff) < 110) -- less than 10% bigger
     where
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<div class='path'>path: <a href='/guix/log/?id=ce9484d85101338d2aa7194155ae232722a9b0f4'>root</a>/<a href='/guix/log/doc?id=ce9484d85101338d2aa7194155ae232722a9b0f4'>doc</a>/<a href='/guix/log/doc/package-hello.scm?id=ce9484d85101338d2aa7194155ae232722a9b0f4'>package-hello.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/doc/package-hello.scm?id=ce9484d85101338d2aa7194155ae232722a9b0f4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2015-09-14 23:10:58 +0200'>2015-09-14</span></td><td><a href='/guix/commit/doc/package-hello.scm?id=17d8e33f316b7e88aa06452f873b59770989f1b6'>doc: Use the recommended Scheme format.</a><span class='msg-avail'>...</span></td><td>Mathieu Lirzin</td></tr>
<tr><td><span title='2015-08-19 22:23:59 -0400'>2015-08-19</span></td><td><a href='/guix/commit/doc/package-hello.scm?id=0d2794005caa627965fd6256f28f94e36cd4b5a0'>scripts: package: Add --install-from-file option.</a><span class='msg-avail'>...</span></td><td>David Thompson</td></tr>