Use the default line length for black ('no configuration')

and update `isort` to a stable configuration given the black line length

pyproject.toml

@@ -1,5 +1,4 @@
 [tool.black]
-line-length = 100
 target_version = ['py37']
 include = '\.pyi?$'
 exclude = '''

tox.ini

@@ -19,7 +19,7 @@ multi_line_output=3
 include_trailing_comma=True
 force_grid_wrap=0
 use_parentheses=True
-line_length=100
+line_length=88
 skip_glob=
     *_pb2*.py
     *.pyi