Update build.gradle

I was facing no lambda support in source 7. To fix it I have added it.

Author: nnrohu

android/build.gradle

@@ -59,6 +59,10 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
         }
     }
+    compileOptions {
+       sourceCompatibility JavaVersion.VERSION_1_8
+       targetCompatibility JavaVersion.VERSION_1_8
+    }
     lintOptions {
         abortOnError false
     }
@@ -157,4 +161,4 @@ afterEvaluate { project ->
             }
         }
     }
-}
+}