Copy all dependencies declared in your .gradle file to "libs" folder.

copyDepsToLibs.gradle

/**
 * Custom task to copy all dependencies declared in you .gradle file
 * to "libs" folder. If their dependencies contains .jar files, this will be released
 * on aar or .jar final file of your project.
 */

task copyLibs(type: Copy) {
    from configurations.compile
    into 'libs'
}

afterEvaluate {
    android.libraryVariants.all { variant ->
        variant.javaCompiler.dependsOn(copyLibs)
    }
}