Revert "flake8: Disable N808"

This reverts commit a14b986326.

Now allowed in pep8-naming 0.15.1.

.flake8

@@ -17,8 +17,6 @@ exclude = .*,__pycache__,resources.py
 #       (for pytest's __tracebackhide__)
 # F401: Unused import
 # N802: function name should be lowercase
-# N808: type variable names should use CapWords convention
-#       (doesn't allow _T as name)
 # N818: exception name '...' should be named with an Error suffix
 # N806: variable in function should be lowercase
 # P101: format string does contain unindexed parameters
@@ -51,7 +49,7 @@ ignore =
     B001,B008,B305,
     E128,E226,E265,E501,E402,E266,E722,E731,
     F401,
-    N802,N808,N818,
+    N802,N818,
     P101,P102,P103,
     D102,D103,D106,D107,D104,D105,D209,D211,D401,D402,D403,D412,D413,
     A003,