Update CodeMirror to version 5.15.3

public/vendor/codemirror/addon/edit/closebrackets.js

@@ -109,7 +109,7 @@
     var ranges = cm.listSelections();
     var opening = pos % 2 == 0;
 
-    var type, next;
+    var type;
     for (var i = 0; i < ranges.length; i++) {
       var range = ranges[i], cur = range.head, curType;
       var next = cm.getRange(cur, Pos(cur.line, cur.ch + 1));