[Android] Bump gradle plugin to 2.1.0

And fix deprecation warning in script

Source/Android/app/build.gradle

@@ -60,14 +60,14 @@ android {
     // of product flavors are paid vs. free, ARM vs. x86, etc.
     productFlavors {
         arm_64 {
-            flavorDimension "abi"
+            dimension "abi"
             ndk {
                 abiFilter "arm64-v8a"
             }
         }
 
         x86_64 {
-            flavorDimension "abi"
+            dimension "abi"
             ndk {
                 abiFilter "x86_64"
             }

Source/Android/build.gradle

@@ -5,7 +5,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:1.5.0'
+        classpath 'com.android.tools.build:gradle:2.1.0'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files