Fix locale directory in MANIFEST.in

Actual location is swift/locale, not locale.

This makes build to not include .mo files if they have been created
previously with compile_catalog.

Change-Id: I907e9bd6dde57cb9ed718656e56a313e82bad128
Closes-Bug: 1583618

Author: amoralej

MANIFEST.in

@@ -6,7 +6,7 @@ include tox.ini
 include requirements.txt test-requirements.txt
 graft doc
 graft etc
-graft locale
+graft swift/locale
 graft test/functional
 graft test/probe
 graft test/unit