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/random.rst

@@ -44,7 +44,7 @@ Example
 The following code will count down from a random even number between 10 and 20 to 1:
 
 ::
- 
+
     for i in (seq (random 10 2 20) -1 1)
         echo $i
     end
@@ -62,5 +62,5 @@ Or, to only get even numbers from 2 to 20::
     random 2 2 20
 
 Or odd numbers from 1 to 3::
-  
+
     random 1 2 3 # or 1 2 4