Include package_data in setup.py

This was causing all conda based builds to fail

MANIFEST.in

@@ -1,4 +1,4 @@
 include *.md
 include LICENSE
 include setup.cfg
-include repo2docker/files/*
+recursive-include repo2docker/files *

setup.py

@@ -17,6 +17,7 @@ setup(
     author_email='yuvipanda@gmail.com',
     license='BSD',
     packages=find_packages(),
+    include_package_data=True,
     entry_points={
         'console_scripts': [
             'jupyter-repo2docker = repo2docker.__main__:main',