I can't find any issue. Try `make clean`, then `make deps` to ensure everything is good. Here's the output from `make maze` on my computer:
fraser-macbookpro:blockly-games fraser$ make maze
Converting messages.js to JSON for Translatewiki.
python build/messages_to_json.py
Converting JSON from Translatewiki to message files.
python build/json_to_js.py
Generated message js files for: ['ab', 'ace', 'af', 'am', 'ar', 'ast', 'az', 'ba', 'be-tarask', 'be', 'bg', 'bn', 'br', 'ca', 'cdo', 'cs', 'da', 'de', 'diq', 'el', 'en', 'eo', 'es', 'et', 'eu', 'fa', 'fi', 'fo', 'fr', 'frr', 'gl', 'gn', 'ha', 'hak', 'he', 'hi', 'hr', 'hrx', 'hu', 'hy', 'ia', 'id', 'ig', 'inh', 'is', 'it', 'ja', 'ka', 'kab', 'kbd-cyrl', 'km', 'kn', 'ko', 'ksh', 'ku-latn', 'ky', 'la', 'lb', 'lki', 'lrc', 'lt', 'lv', 'mg', 'mk', 'ml', 'ms', 'my', 'mzn', 'nb', 'ne', 'nl', 'oc', 'olo', 'pa', 'pl', 'pms', 'ps', 'pt-br', 'pt', 'ro', 'ru', 'sc', 'sco', 'sd', 'si', 'sk', 'skr-arab', 'sl', 'smn', 'sq', 'sr-latn', 'sr', 'sv', 'sw', 'ta', 'tcy', 'te', 'th', 'ti', 'tr', 'uk', 'ur', 'uz', 'vi', 'yo', 'yue', 'zh-hans', 'zh-hant']
python build/compress.py maze
Compressing Maze
third-party/closurebuilder/closurebuilder.py: Scanning paths...
third-party/closurebuilder/closurebuilder.py: 770 sources scanned.
third-party/closurebuilder/closurebuilder.py: Building dependency tree..
Found 157 dependencies.
Compressed to 246 KB.
Found 32 Blockly messages.
Found 45 Blockly Games messages.
fraser-macbookpro:blockly-games fraser$ ls -lag appengine/maze/generated/
total 520
drwxr-xr-x 5 primarygroup 160 Sep 26 23:50 .
drwxr-xr-x 27 primarygroup 864 Sep 26 23:50 ..
-rw-r--r-- 1 primarygroup 252765 Sep 26 23:50 compressed.js
drwxr-xr-x 66 primarygroup 2112 Sep 26 23:51 msg
-rw-r--r-- 1 primarygroup 8690 Sep 26 23:50 uncompressed.js