Force requirement of nd_service_registry 0.2.5, and bump ver to 0.3.2.

nd_service_registry has a major bug
(https://github.com/Nextdoor/ndserviceregistry/issues/19) that needs to
be pushed out. This forces new installations of zk_watcher >= 0.3.2 to
get the bug-fixed version of nd_service_registry.

Change-Id: I6f964e0cd6f9dfd95efd9ebd6f4247cdb0fe16b9