Documentation/git-worktree: fix incorrect reference to file "locked"

The administrative file to suppress pruning is named "locked", not "lock".

[es: don't touch unrelated "git worktree lock" command; reword commit
message]

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -39,7 +39,7 @@ repository so that they do not get automatically pruned.
 
 If a linked working tree is stored on a portable device or network share
 which is not always mounted, you can prevent its administrative files from
-being pruned by creating a file named 'lock' alongside the other
+being pruned by creating a file named 'locked' alongside the other
 administrative files, optionally containing a plain text reason that
 pruning should be suppressed. See section "DETAILS" for more information.