Remove trailing whitespace before newlines

[no-reply]

One final fix to the whitespace normalizer. We want to destroy trailing whitespace on each line, not only for the entire string.

Connected to #362.

[coveralls]

Coverage increased (+0.07%) to 89.821% when pulling 3ff14c5e40eb348b10457b508270800c594a6732 on trailing-whitespace into 189021210a2e21879891b427a978814e49830455 on master.