Documentation/email-clients.txt: remove trailing whitespace

Signed-off-by: NLuis de Bethencourt <luisbg@osg.samsung.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/email-clients.txt

@@ -220,7 +220,7 @@ to coerce it into behaving.
   Compose dialog.
 
   Please note that "external editor" requires that your editor must not
-  fork, or in other words, the editor must not return before closing. 
+  fork, or in other words, the editor must not return before closing.
   You may have to pass additional flags or change the settings of your
   editor. Most notably if you are using gvim then you must pass the -f
   option to gvim by putting "/usr/bin/gvim -f" (if the binary is in