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/function.rst

@@ -85,7 +85,7 @@ will run the ``ls`` command, using the ``-l`` option, while passing on any addit
     # prints: [DEBUG] foo: bar
 
     # OR
-    
+
     function debug2 -a var
         echo [DEBUG] $var: $$var >&2
     end
@@ -106,7 +106,7 @@ will create a ``debug`` command to print chosen variables to `stderr`.
         if test $status = 0
             switch $argv[(count $argv)]
                 case '-*'
-    
+
                 case '*'
                     cd $argv[(count $argv)]
                     return
@@ -124,7 +124,7 @@ This will run the ``mkdir`` command, and if it is successful, change the current
     function notify
         set -l job (jobs -l -g)
         or begin; echo "There are no jobs" >&2; return 1; end
-    
+
         function _notify_job_$job --on-job-exit $job --inherit-variable job
             echo -n \a # beep
             functions -e _notify_job_$job