Fix spelling in style guide

Author: thomasballinger

docs/writing/style.rst

@@ -9,7 +9,7 @@ recognised fact that code is read much more often than it is written.
 One reason for Python code to be easily read and understood is its relatively
 complete set of Code Style guidelines and "Pythonic" idioms.
 
-Moreover, when a veteran Python developer (a Pythonistas) point to some
+Moreover, when a veteran Python developer (a Pythonista) point to some
 parts of a code and say it is not "Pythonic", it usually means that these lines
 of code do not follow the common guidelines and fail to express the intent in
 what is considered the best (hear: most readable) way.
@@ -178,7 +178,7 @@ possibilities, because it grows the confidence that no hard-wall will be on the
 way.  However, knowing how to use them and particularly when **not** to use
 them is the most important.
 
-Like a Kungfu master, a pythonistas knows how to kill with a single finger, and
+Like a Kungfu master, a Pythonista knows how to kill with a single finger, and
 never do it.
 
 We are all consenting adults