Update install-gradle.sh

Change to Gradle 1.9
Update wercker-box.yml

Change to Gradle 1.9
Update README.md

Change Gradle version.
Update install-sdk.sh

Included Android Build Tools 19.0.1
Update wercker-box.yml

Change box version to 0.0.20
Merge pull request #1 from aeciobf/master

Update box with gradle 1.9 &  build tools 19.0.1