Build fails with non-default project directory

[MichaelElmore1]

When using a different directory, build fails with the reason "The 'java' plugin has been applied, but it is not compatible with the Android plugins." This is likely due to this line: https://github.com/opensensorhub/osh-android/blob/master/build.gradle#L27

Steps to reproduce:
Clone osh-android as osh-android-test
Change to v2 branch
Run git submodule update --init --recursive if necessary
Load Gradle changes

Theoretically, it is an easy fix, but I don't know the Gradle syntax for getting the app root directory programmatically.