Do not publish tests inside the npm package

Summary:
I'm removing the `src/test` folder from the npm bundle as it's not really
needed for the sake of distributing the gradle plugin.

Changelog:
[Internal] [Changed] - Do not publish tests inside the react-native-gradle-plugin npm package

Reviewed By: ShikaSD

Differential Revision: D31956449

fbshipit-source-id: b84138d24a7c51c44b92ebfc84f35afb3668dee5

packages/react-native-gradle-plugin/package.json

@@ -20,7 +20,7 @@
     "gradle",
     "gradlew",
     "gradlew.bat",
-    "src",
+    "src/main",
     "README.md"
   ],
   "dependencies": {