Some issue with Java

[rocboronat]

It seems that there's some issue with using Java 7 in the Docker image.

FAILURE: Build failed with an exception.

* Where:
Build file '/workspace/app/build.gradle' line: 16

* What went wrong:
A problem occurred evaluating project ':app'.
> java.lang.UnsupportedClassVersionError: com/android/build/gradle/AppPlugin : U                                                                                         nsupported major.minor version 52.0

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug                                                                                          option to get more log output.

BUILD FAILED