JVMCBC-103: Depend on RxJava 1.0.4

Motivation
----------
HEAD is currently depending on 1.0.3, which contains critical fixes
for timeouts. Since we are upgrading RxJava anyways, going to the
last released version possible on 1.0 makes sure we cover as many
bugfixes as possible.

Change-Id: I2e821797b81ca0f415d61788bb3736a6f13055cc
Reviewed-on: http://review.couchbase.org/44760
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Simon Baslé <simon@couchbase.com>