Change dialyzer file path

So that it guarantees there's no dialyzer plt file versioning
issues when the same bot is used to run dialyzer for different
branches of couchdb.

Change-Id: I3e8ee4df225eefaae9077954e7718ab7e43d1a77
Reviewed-on: http://review.couchbase.org/25354
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>