title: create-react-native-app displays new warnings
body: <p>Creating a new app with create-react-native-app is now generating new warnings.  Is there anything I need to do to correct the warnings?  For instance, how would I update the components listed:</p>
  
  <pre><code> ExpoRootComponent, RootErrorBoundary, Text, View
  </code></pre>
  
  <p>here are the new warnings:  (can all this be ignored? will create-react-native-app be updated to use 0.55.x?)</p>
  
  <pre><code>14:30:04: Warning: componentWillMount is deprecated and will be removed in 
  the next major version. Use componentDidMount instead. As a temporary 
  workaround, you can rename to UNSAFE_componentWillMount.
  
  Please update the following components: ExpoRootComponent, 
  RootErrorBoundary, Text, View
  
  Learn more about this warning here:
  xxx:/fb.me/react-async-component-lifecycle-hooks
  - node_modules\react-native\Libraries\ReactNative\YellowBox.js:82:15 in warn
  - node_modules\react-native\Libraries\Renderer\ReactNativeRenderer- 
  dev.js:5706:19 in printWarning
  - ... 21 more stack frames from framework internals
  14:30:06: Warning: componentWillReceiveProps is deprecated and will be 
  removed in the next major version. Use static getDerivedStateFromProps 
  instead.
  
  Please update the following components: Text, View
  
  Learn more about this warning here:
  xxx:/fb.me/react-async-component-lifecycle-hooks
  - node_modules\react-native\Libraries\ReactNative\YellowBox.js:82:15 in warn
  - node_modules\react-native\Libraries\Renderer\ReactNativeRenderer- 
  dev.js:5706:19 in printWarning
  - ... 21 more stack frames from framework internals
  </code></pre>