doc: pull-fetch-param typofix

An earier patch had a typo discovered after it has been merged to
'next'.  Fix it.

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Jean-Noël Avila via GitGitGadget

Documentation/pull-fetch-param.adoc

@@ -91,7 +91,7 @@ object.
 When the remote branch you want to fetch is known to
 be rewound and rebased regularly, it is expected that
 its new tip will not be a descendant of its previous tip
-(as stored in your remote-tracking branch the last time_
+(as stored in your remote-tracking branch the last time
 you fetched).  You would want
 to use the `+` sign to indicate non-fast-forward updates
 will be needed for such branches.  There is no way to