sopel: Update to check for proper UTF8 on Windows

The locale.getlocale() check currently looks for UTF-8 only, however
on windows with powershell and UTF8 enabled the return value is utf8
so this check still fails.

sopel/__init__.py

@@ -34,7 +34,7 @@
 ]
 
 loc = locale.getlocale()
-if not loc[1] or 'UTF-8' not in loc[1]:
+if not loc[1] or ('UTF-8' not in loc[1] and 'utf8' not in loc[1]):
     print('WARNING!!! You are running with a non-UTF8 locale environment '
           'variable (e.g. LC_ALL is set to "C"), which makes Python 3 do '
           'stupid things. If you get strange errors, please set it to '