editorconfig / doc_src: trim trailing whitespace

Commit 0893134543 (Added .editorconfig file (#3332) (#3313),
2016-08-25) trimmed trailing whitespace  for Markdown file (which do
have significant trailing whitespace) but ReStructuredText does not,
and none of our Markdown files cares about this, so let's clean up
whitespace always.

doc_src/cmds/alias.rst

@@ -46,12 +46,12 @@ The following code will create ``rmi``, which runs ``rm`` with additional argume
 ::
 
     alias rmi="rm -i"
-    
+
     # This is equivalent to entering the following function:
     function rmi --wraps rm --description 'alias rmi=rm -i'
         rm -i $argv
     end
-    
+
 ``alias`` sometimes requires escaping, as you can see here::
 
     # This needs to have the spaces escaped or "Chrome.app..."