runtime(doc): remove trailing whitespace in cmdline.txt

Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: chrisbra

runtime/doc/cmdline.txt

@@ -379,7 +379,7 @@ terminals)
 
 :keepp[atterns] {command}			*:keepp* *:keeppatterns*
 		Execute {command}, without adding anything to the search
-		history and, in case of the the |:s| and |:&| command, without 
+		history and, in case of the the |:s| and |:&| command, without
 		modifying the last substitute pattern and substitute string.
 
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