[gfm mode] Simplify URL regexp, since it's crashing Chrome

Issue #1160

mode/gfm/gfm.js

@@ -75,9 +75,10 @@ CodeMirror.defineMode("gfm", function(config) {
           return "link";
         }
       }
-      if (stream.match(/^((?:[a-z][\w-]+:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))/i)) {
+      if (stream.match(/^((?:[a-z][\w-]+:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+|\([^\s()<>]*\))+(?:\([^\s()<>]*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))/i)) {
         // URLs
         // Taken from http://daringfireball.net/2010/07/improved_regex_for_matching_urls
+        // And then (issue #1160) simplified to make it not crash the Chrome Regexp engine
         return "link";
       }
       stream.next();