update flake8 config

Author: jorisvandenbossche

setup.cfg

@@ -12,10 +12,11 @@ tag_prefix = v
 parentdir_prefix = pandas-
 
 [flake8]
-max-line-length = 79
+max-line-length = 88
 ignore =
+    E501,  # longer line length
     W503,  # line break before binary operator
-    W504,  # line break after binary operator
+    E203,  # space before : (needed for how black formats slicing)
     E402,  # module level import not at top of file
     E731,  # do not assign a lambda expression, use a def
     C406,  # Unnecessary list literal - rewrite as a dict literal.