Fix whitespace

Author: tomasr8

Doc/howto/argparse.rst

@@ -815,7 +815,7 @@ For instance, in this :mod:`argparse` output:
      -q, --quiet
 
 The strings ``usage:``, ``positional arguments:``, ``options:`` and
-``show this help message and exit`` are all translatable. 
+``show this help message and exit`` are all translatable.
 
 In order to translate these strings, they must first be extracted
 into a ``.po`` file. For example, using `Babel <https://babel.pocoo.org/>`__,