changed task directory in build.gradle

my project wouldn't build with:
```groovy
    from android.sourceSets.main.java
```
this [SO post] led me toward this a solution. (http://stackoverflow.com/questions/26787490/gradle-2-1-error-cannot-convert-the-provided-notation-to-a-file-or-uri-src-main)

possible all due to me using the latest gradle version 2.2.1