apply: Use the term "working tree" consistently

The documentation for 'git apply' uses both the terms
"work tree" and "working tree". Since the glossary uses
the term "working tree", change all occurrences of
"work tree" to "working tree".

Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-apply.txt

@@ -51,15 +51,15 @@ OPTIONS
 
 --check::
 	Instead of applying the patch, see if the patch is
-	applicable to the current work tree and/or the index
+	applicable to the current working tree and/or the index
 	file and detects errors.  Turns off "apply".
 
 --index::
 	When `--check` is in effect, or when applying the patch
 	(which is the default when none of the options that
 	disables it is in effect), make sure the patch is
 	applicable to what the current index file records.  If
-	the file to be patched in the work tree is not
+	the file to be patched in the working tree is not
 	up-to-date, it is flagged as an error.  This flag also
 	causes the index file to be updated.