Bump Gradle version to 2.3
Bump Gradle version to 2.3

Marc-Calis/shimmer,openmhealth/shimmer,smalldatalab/omh-shims,openmhealth/shimmer,Marc-Calis/shimmer,smalldatalab/omh-shims,Marc-Calis/shimmer,smalldatalab/omh-shims,openmhealth/shimmer,smalldatalab/omh-shims,openmhealth/shimmer,Marc-Calis/shimmer