black --diff so user knows what to fix

Author: dhimmel

.travis.yml

@@ -15,7 +15,8 @@ install:
   - python setup.py sdist bdist_wheel
 script:
   - pytest --verbose --color=yes
-  - black --check .
+  # if the following command fails, run `black .` locally to reformat the code
+  - black --check --diff .
   # temporary workaround for portray "Module not found" error https://git.io/JeR9C
   - export PYTHONPATH=.
   - portray as_html --overwrite --output_dir=docs

manubot/process/tests/test_bibliography.py

@@ -2,11 +2,7 @@
 
 import pytest
 
-from manubot.pandoc.tests.test_bibliography import (
-    bibliography_paths  # list of 4 paths: 'bibliography.bib', 'bibliography.json',
-    # 'bibliography.nbib', 'bibliography.ris'
-    ,
-)
+from manubot.pandoc.tests.test_bibliography import bibliography_paths
 from manubot.process.bibliography import load_manual_references