Documentation/git-worktree: fix broken 'linkgit' invocation

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sunshineco

Documentation/git-worktree.txt

@@ -27,7 +27,7 @@ bare repository) and zero or more linked working trees.
 When you are done with a linked working tree you can simply delete it.
 The working tree's administrative files in the repository (see
 "DETAILS" below) will eventually be removed automatically (see
-`gc.worktreePruneExpire` in linkgit::git-config[1]), or you can run
+`gc.worktreePruneExpire` in linkgit:git-config[1]), or you can run
 `git worktree prune` in the main or any linked working tree to
 clean up any stale administrative files.