Update project to use Gradle's plugins{} block

Summary:
This project was still using the legacy Gradle's "apply:" syntax
to apply Gradle Plugins. I'm changing it here to use instead the
`plugins{}` block as it make easier to apply other plugins for publishing later.

Reviewed By: mdvacca

Differential Revision: D46330014

fbshipit-source-id: 5483a717a62d5ab76749026c5203dc96a35d73e7

sample/build.gradle

@@ -5,7 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-apply plugin: 'com.android.application'
+plugins {
+    id("com.android.application")
+}
 
 android {
     namespace 'com.facebook.yoga.sample'