modify stackforge/swift3 to openstack/swift3

As swift3.git has move from stackforge/swift3 to openstack/swift3,
so modify it.

Change-Id: Ieaff4c93889c46c7d4b8ecada1a5d7cf3c775965
diff --git a/stackrc b/stackrc
index a164335..4026ff8 100644
--- a/stackrc
+++ b/stackrc
@@ -447,7 +447,7 @@
 GITBRANCH["keystonemiddleware"]=${KEYSTONEMIDDLEWARE_BRANCH:-master}
 
 # s3 support for swift
-SWIFT3_REPO=${SWIFT3_REPO:-${GIT_BASE}/stackforge/swift3.git}
+SWIFT3_REPO=${SWIFT3_REPO:-${GIT_BASE}/openstack/swift3.git}
 SWIFT3_BRANCH=${SWIFT3_BRANCH:-master}
 
 # ceilometer middleware