fix: Disable test "can read previous version's cache"

This test is currently broken as a current version of stacker
cannot read an old version's cache.  The change was intended,
to clean up /stacker under c68147c.

Signed-off-by: Scott Moser <smoser@brickies.net>

test/caching.bats

@@ -185,6 +185,8 @@ EOF
 }
 
 @test "can read previous version's cache" {
+    skip "old does not work as a cache due to stacker/import change in c68147cba8d"
+
     # some additional testing that the cache can be read by older versions of
     # stacker (cache_test.go has the full test for the type, this just checks
     # the mechanics of filepaths and such)