Revert "Allow trailing whitespace, since Flake8 complains about trail…

…ing whitespace in strings and docstrings. Trailing whitespace in code will be catched by the black check anyway."

This reverts commit 0474556.

On second thoughts, the error output from black will be much worse, so it should be better to keep it.

tox.ini

@@ -3,7 +3,7 @@ envlist = py{36,37,38,39}
 
 [flake8]
 extend-exclude = build,examples/issue_*.py
-ignore = E741,F401,W503,E402,E501,E731,E713,E203,W291,W293
+ignore = E741,F401,W503,E402,E501,E731,E713,E203
 per-file-ignores =
     locust/test/*: F841
     examples/*: F841