title: Set buildTypes shows error Activity class does not exist
body: <p>I want to set different environment on android with react native.</p>
  <p>Step 1 create project:</p>
  <p>Create a pure react native project <code>&quot;react-native&quot;: &quot;0.64.0&quot;,</code></p>
  <p>Step 2 add an environment releasestaging under android/app/build.gradle:</p>
  <pre><code>buildTypes{      
     //... 
      releasestaging {
              initWith release    
              applicationIdSuffix &quot;.releasestaging&quot; 
              matchingFallbacks =  ['release']
          }
    // ...
  }
  </code></pre>
  <p>Step 3  type cpmmand on terminal:</p>
  <pre><code>npx react-native run-android --variant=releasestaging
  </code></pre>
  <p>build result shows the error:</p>
  <pre><code>BUILD SUCCESSFUL in 5s
  46 actionable tasks: 46 executed
  info Connecting to the development server...
  info Starting the app on &quot;emulator-5554&quot;...
  Starting: Intent { cmp=com.testenvone/.MainActivity }
  Error type 3
  Error: Activity class {com.testenvone/com.testenvone.MainActivity} does not exist.
  </code></pre>
  <p>Any one knows what step I miss ? Thanks.</p>