Fixing javadoc artifact generation

[SebastianEngel]

jar contained only META-INF previously

[daimajia]

@SebastianEngel
Really helpful PR, while I met another error I have no idea how to handle it.

:demo:test
:demo:check
:demo:build
:library:androidJavadocs/home/travis/build/daimajia/AndroidImageSlider/library/src/main/java/com/daimajia/slider/library/SliderLayout.java:6: error: package android.support.v4.view does not exist
import android.support.v4.view.PagerAdapter;
                              ^
/home/travis/build/daimajia/AndroidImageSlider/library/src/main/java/com/daimajia/slider/library/Tricks/InfiniteViewPager.java:4: error: package android.support.v4.view does not exist
import android.support.v4.view.PagerAdapter;

When building javadoc, it can not find the dependencies doc.

Do you have any suggestion on this?

[AlexanderLS]

@SebastianEngel @daimajia your commits merged to https://github.com/Vorlonsoft/GradleMavenPush