title: `react-native run-ios` command fails (PCH issues), but build succeeds in xcode
body: <p>I had a react native project that was building and running perfectly fine. Then I decided to move it into a sub directory, and I started receiving lots of precompiled header errors: </p>
  
  <pre><code>PCH was compiled with module cache path '/Users/me/place1/ios/build/ModuleCache/3R9LOJFOBFZVJ', but the path is currently
    '/Users/me/place2/app/ios/build/ModuleCache/3R9LOJFOBFZVJ'
  </code></pre>
  
  <p>Fair enough, but what's weird is that, if I open up the xcode project and clean / rebuild in there, everything works!</p>
  
  <p>Then when I close down the server started by xcode and try to launch it using <code>react-native run-ios</code> it continues to complain about PCH issues.</p>
  
  <p>Not sure what I'm missing...</p>