Add F841 to flake8 ignore list

Author: sgibson91

.flake8

@@ -6,5 +6,6 @@
 # E402: module level import not at top of file
 # I100: Import statements are in the wrong order
 # I101: Imported names are in the wrong order. Should be
-ignore = E, C, W, I100, I101, D400
+# F841: local variable ... is assigned to but never used
+ignore = E, C, W, I100, I101, D400, F841
 builtins = c