Compile with Java 8 support for using Retrolambda

app/build.gradle

@@ -16,6 +16,11 @@ android {
         versionName "1.0"
     }
 
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
     buildTypes {
         release {
             minifyEnabled false