Fix typo in bin/check-merged.sh

Change-Id: I7ca06602179e35d5ce86879b1081299a841feba9
Reviewed-on: https://gerrit.libreoffice.org/12431Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

bin/check-merged.sh

 #! /bin/bash
 #
-# check that master contains all the patches from a brach
+# check that master contains all the patches from a branch
 # and list those that are missing
 #