Fixing androidJavadocs and androidSourcesJar tasks

See https://code.google.com/p/android/issues/detail?id=71174 and
https://android.googlesource.com/platform/tools/base/+/5e71a83f74258b85d
7f5306bf743c4d69d6242f8%5E%21/#F2
Merge pull request #36 from SebastianEngel/master

Fixing androidJavadocs and androidSourcesJar tasks
Fix androidJavadocs

Converting class com.android.build.gradle.internal.api.DefaultAndroidSourceDirectorySet to File using toString() method has been deprecated and is scheduled to be removed in Gradle 2.0. Please use java.io.File, java.lang.String, java.net.URL, or java.net.URI instead.
Merge pull request #38 from grantland/master

Fix androidJavadocs