Backport PR #28614: CI: troubleshoot s3fs failures (#28615)

Author: meeseeksmachine

ci/deps/travis-36-cov.yaml

@@ -29,7 +29,7 @@ dependencies:
   - python-snappy
   - python=3.6.*
   - pytz
-  - s3fs
+  - s3fs<0.3
   - scikit-learn
   - scipy
   - sqlalchemy

ci/deps/travis-36-slow.yaml

@@ -18,7 +18,7 @@ dependencies:
   - python-dateutil
   - python=3.6.*
   - pytz
-  - s3fs
+  - s3fs<0.3
   - scipy
   - sqlalchemy
   - xlrd

ci/deps/travis-37.yaml

@@ -17,7 +17,7 @@ dependencies:
   - pytest-xdist
   - pytest-mock
   - hypothesis>=3.58.0
-  - s3fs
+  - s3fs<0.3
   - pip
   - pyreadstat
   - pip:

pandas/tests/groupby/test_categorical.py

@@ -782,7 +782,7 @@ def test_categorical_no_compress():
 
 def test_sort():
 
-    # http://stackoverflow.com/questions/23814368/sorting-pandas-categorical-labels-after-groupby  # noqa: flake8
+    # http://stackoverflow.com/questions/23814368/sorting-pandas-categorical-labels-after-groupby  # noqa: E501
     # This should result in a properly sorted Series so that the plot
     # has a sorted x axis
     # self.cat.groupby(['value_group'])['value_group'].count().plot(kind='bar')