Switch to nightly tag for release image (#1746)

as tests for connext rmw have been disabled.54

.dockerhub/release/hooks/build

 #!/bin/bash
 set -ex
 
-export FROM_IMAGE=osrf/ros2:nightly-rmw-nonfree
+export FROM_IMAGE=osrf/ros2:nightly
 export FAIL_ON_BUILD_FAILURE=""
 export UNDERLAY_MIXINS="release ccache"
 export OVERLAY_MIXINS="release ccache"