title: Flutter Unable to merge dex
body: <p>I'm using last version of flutter.</p>
  
  <p><strong>Error :</strong></p>
  
  <pre><code>FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
  &gt; java.lang.RuntimeException: java.lang.RuntimeException: com.android.builder.dexing.DexArchiveMergerException: Unable to merge dex
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
  
  * Get more help at https://help.gradle.org
  
  BUİLD FAILED in 3s
  Finished with error: Gradle build failed: 1
  </code></pre>
  
  <p>pubspec.yaml dependencies, using firebase_auth ^0.5.20 :</p>
  
  <pre><code>dependencies:
    flutter:
      sdk: flutter
    intl: ^0.15.7
    cloud_firestore: ^0.7.3
    firebase_database: ^1.0.4
    cached_network_image: ^0.4.2
    firebase_auth: ^0.5.20
  cupertino_icons: ^0.1.2
  </code></pre>
  
  <p>android app build.gradle default config:</p>
  
  <pre><code>android{
  defaultConfig {
          applicationId "com.example.flutterapp"
          minSdkVersion 21
          targetSdkVersion 27
          versionCode flutterVersionCode.toInteger()
          versionName flutterVersionName
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
          multiDexEnabled true
      }
  }
  </code></pre>