[nanobox] Add python for node-gyp (#3491)

Needed since merge of #3067.

boxfile.yml

@@ -14,9 +14,12 @@ run.config:
     # for videos:
     - ffmpeg3
 
-    # to prep the .env file
+    # to prep the .env file:
     - gettext-tools
 
+    # for node-gyp, used in the asset compilation process:
+    - python-2
+
   cache_dirs:
     - node_modules