Detect waf wscript files as Python

Detect the waf build system's wscript files as Python.
https://waf.io/

Author: Michael Vincent

identify/extensions.py

@@ -294,4 +294,5 @@
     'Rakefile': EXTENSIONS['rb'],
     'setup.cfg': EXTENSIONS['ini'],
     'WORKSPACE': EXTENSIONS['bzl'],
+    'wscript': EXTENSIONS['py'],
 }