Fix typo in git-gc document.

The variable gc.packrefs for git-gc can be set to true, false and
"notbare", not "nobare".
Signed-off-by: NJiang Xin <jiangxin@ossxp.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -971,7 +971,7 @@ gc.packrefs::
 	Running `git pack-refs` in a repository renders it
 	unclonable by Git versions prior to 1.5.1.2 over dumb
 	transports such as HTTP.  This variable determines whether
-	'git gc' runs `git pack-refs`. This can be set to `nobare`
+	'git gc' runs `git pack-refs`. This can be set to `notbare`
 	to enable it within all non-bare repos or it can be set to a
 	boolean value.  The default is `true`.
 

Documentation/git-gc.txt

@@ -107,7 +107,7 @@ how long records of conflicted merge you have not resolved are
 kept.  This defaults to 15 days.
 
 The optional configuration variable 'gc.packrefs' determines if
-'git gc' runs 'git pack-refs'. This can be set to "nobare" to enable
+'git gc' runs 'git pack-refs'. This can be set to "notbare" to enable
 it within all non-bare repos or it can be set to a boolean value.
 This defaults to true.