title: Firebase authentication issues on my project
body: <p>I have linked Firebase authentication to my project but I still keep getting the error : </p>
  
  <p>The app gradle file must have a dependency on <code>com.google.firebase:firebase-core for Firebase services to work as intended.</code>    </p>
  
  <p>I have followed all instruction still no luck.
  Please have a look at the code and let me know what else i need to add</p>
  
  <pre><code>apply plugin: 'com.android.application'
  apply plugin: 'com.google.gms.google-services'
  
  android {
       compileSdkVersion 28
       defaultConfig {
          applicationId "com.nis.taxiapp1"
          minSdkVersion 15
          targetSdkVersion 28
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner 
  "android.support.test.runner.AndroidJUnitRunner"
      }
       buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android- 
   optimize.txt'), 'proguard-rules.pro'
          }
       }
   }
  
  dependencies {
  implementation fileTree(dir: 'libs', include: ['*.jar'])
  implementation 'com.android.support:appcompat-v7:28.0.0'
  implementation 'com.android.support.constraint:constraint-layout:1.1.3'
  implementation 'com.google.firebase:firebase-auth:16.0.3'
  
  testImplementation 'junit:junit:4.12'
  androidTestImplementation 'com.android.support.test:runner:1.0.2'
  androidTestImplementation 'com.android.support.test.espresso:espresso- 
     core:3.0.2'
      }
        apply plugin: 'com.google.gms.google-services'
  </code></pre>
  
  <p>My project Gradle code: </p>
  
  <pre><code>buildscript {
      repositories {
          google()
          jcenter() 
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:3.3.1'
          classpath 'com.google.gms:google-services:4.1.0'
      }
  }
  
  allprojects {
      repositories {
          google()
          jcenter()
      }
   }
  
   task clean(type: Delete) {
      delete rootProject.buildDir
   }`
  </code></pre>