JVMCBC-36: Update RxJava to RC3

Change-Id: I6defc3f7e3c72b8549d1f3390f7fac0c33c09e3f
Reviewed-on: http://review.couchbase.org/41435
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>