title: Unable to find a specification for `React-Core` depended upon by `UMReactNativeAdapter`
body: <p>Getting below error, </p>
  
  <pre><code>Analyzing dependencies
  Fetching podspec for `DoubleConversion` from `../node_modules/react-native/third-party-podspecs/DoubleConversion.podspec`
  Pre-downloading: `ExpoKit` from `http://github.com/expo/expo.git`, tag `ios/2.13.0`
  Fetching podspec for `Folly` from `../node_modules/react-native/third-party-podspecs/Folly.podspec`
  Fetching podspec for `glog` from `../node_modules/react-native/third-party-podspecs/glog.podspec`
  [!] Unable to find a specification for `React-Core` depended upon by `UMReactNativeAdapter`
  
  You have either:
   * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
   * mistyped the name or version.
   * not added the source repo that hosts the Podspec to your Podfile.
  </code></pre>
  
  <p>I tried,</p>
  
  <pre><code>pod setup
  pod install
  pod install --repo-update
  </code></pre>
  
  <p>Also, I uninstalled/installed <code>cocoapods</code> again, but still getting above error.</p>