Added gradle task to produce sources jar

Author: jitpack-io

library/build.gradle

@@ -22,3 +22,12 @@ android {
 dependencies {
     compile fileTree(dir: 'libs', include: ['*.jar'])
 }
+
+task sourcesJar(type: Jar) {
+    from android.sourceSets.main.java.srcDirs
+    classifier = 'sources'
+}
+
+artifacts {
+    archives sourcesJar
+}