black doesn't seem to be working on pypy...

so I am committing an "env" command to the travis script to see what environment variables are available to me to check before running `black`, so I can only run black on non-pypy versions.

Author: radix

.travis.yml

@@ -12,6 +12,7 @@ install:
     - pip install sphinx sphinx_rtd_theme
 script:
     - flake8
+    - env
     - black --check .
     - pytest
     - make doc