doc: fix small typo in git show-branch

Fix small typo as in document <glob> is used not <globs>.

Signed-off-by: Saulius Gurklys <s4uliu5@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: s4uliu5

Documentation/git-show-branch.txt

@@ -19,7 +19,7 @@ DESCRIPTION
 -----------
 
 Shows the commit ancestry graph starting from the commits named
-with <rev>s or <globs>s (or all refs under refs/heads
+with <rev>s or <glob>s (or all refs under refs/heads
 and/or refs/tags) semi-visually.
 
 It cannot show more than 29 branches and commits at a time.