Add pkg_resources._vendor.packaging to freeze.py.

Workaround for https://bitbucket.org/anthony_tuininga/cx_freeze/issues/175/
Also see https://github.com/pyinstaller/pyinstaller/issues/1773

This hopefully fixes AppVeyor builds.

scripts/dev/freeze.py

@@ -86,7 +86,7 @@ def get_build_exe_options(skip_html=False):
         'include_msvcr': True,
         'includes': [],
         'excludes': ['tkinter'],
-        'packages': ['pygments'],
+        'packages': ['pygments', 'pkg_resources._vendor.packaging'],
     }