clean up `TreeWalker.pop()` (#2195)

Remove superfluous parameter.

1 files changed, 3 insertions, 4 deletions

diff --git a/lib/ast.js b/lib/ast.js
index 2972b7aa..0918574d 100644
--- a/lib/ast.js
+++ b/lib/ast.js
@@ -859,7 +859,7 @@ TreeWalker.prototype = {
         if (!ret && descend) {
             descend.call(node);
         }
-        this.pop(node);
+        this.pop();
         return ret;
     },
     parent: function(n) {
@@ -873,9 +873,8 @@ TreeWalker.prototype = {
         }
         this.stack.push(node);
     },
-    pop: function(node) {
-        this.stack.pop();
-        if (node instanceof AST_Lambda) {
+    pop: function() {
+        if (this.stack.pop() instanceof AST_Lambda) {
             this.directives = Object.getPrototypeOf(this.directives);
         }
     },