title: react-native run-android doesn't build
body: <p>I'm totally new in react-native and have an Android emulator running but it doesn't build react-native &amp; shows this error...
  what should i do?</p>
  
  <blockquote>
    <p>FAILURE: Build failed with an exception.</p>
    
    <ul>
    <li>What went wrong:
    Could not resolve all files for configuration ':app:debugCompileClasspath'.
    Could not download appcompat-v7.aar (com.android.support:appcompat-v7:28.0.0)
    Could not get resource '<a href="https://dl.google.com/dl/android/maven2/com/android/support/appcompat-v7/28.0.0/appcompat-v7-28.0.0.aar" rel="nofollow noreferrer">https://dl.google.com/dl/android/maven2/com/android/support/appcompat-v7/28.0.0/appcompat-v7-28.0.0.aar</a>'.
    Connection reset
    Could not download support-fragment.aar (com.android.support:support-fragment:28.0.0)
    Could not get resource </li>
    <li><p>Try:
    Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.</p></li>
    <li><p>Get more help at <a href="https://help.gradle.org" rel="nofollow noreferrer">https://help.gradle.org</a></p></li>
    </ul>
    
    <p>BUILD FAILED in 8m 56s
    1 actionable task: 1 executed
    error Could not install the app on the device, read the error above for details.
    Make sure you have an Android emulator running or a device connected and have
    set up your Android development environment:
    <a href="https://facebook.github.io/react-native/docs/getting-started.html" rel="nofollow noreferrer">https://facebook.github.io/react-native/docs/getting-started.html</a>
    error Command failed: gradlew.bat app:installDebug. Run CLI with --verbose flag for more details.</p>
  </blockquote>