Add noqa rule for trailing whitespace

Author: martin-martin

pep8-beautiful-code/trailing_whitespace.py

@@ -1,7 +1,7 @@
 # Uncomment the code below
 # for an example of code with a trailing whitespace:
 
-# x = 1 + 2 + \ 
+# x = 1 + 2 + \  # noqa w291
 # 3 + 4
 
 # print(x)