title: failed to resolve: com.google.firebase:firebase-core:16.0.0
body: <p>i have android project 
  and i want to add push notifications to that app using google firebase 
  first i downloaded the xml file and past it on app root then
  i added this lines as they said on this link</p>
  
  <pre><code>buildscript {
    dependencies {
      // Add this line
      classpath 'com.google.gms:google-services:4.0.0'
    }
  }
      dependencies {
    // Add this line
    compile 'com.google.firebase:firebase-core:16.0.0'
  }
  ...
  // Add to the bottom of the file
  apply plugin: 'com.google.gms.google-services'
  </code></pre>
  
  <p>and i click sync now 
  always gat this error </p>
  
  <pre><code>failed to resolve: com.google.firebase:firebase-core:16.0.0
  </code></pre>
  
  <p>thank for help
  this is the full gradle file </p>
  
  <pre><code>    apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 25
      buildToolsVersion "28.0.0"
      defaultConfig {
          applicationId "com.softya.demo"
          minSdkVersion 15
          targetSdkVersion 25
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
          exclude group: 'com.android.support', module: 'support-annotations'
      })
      compile 'com.android.support:appcompat-v7:25.3.1'
      compile 'com.android.support:support-v4:25.3.1'
      testCompile 'junit:junit:4.12'
      compile 'com.google.firebase:firebase-core:16.0.0'
  }
  apply plugin: 'com.google.gms.google-services'
  </code></pre>
  
  <p>and this is the gradle file code </p>
  
  <pre><code>    // Top-level build file where you can add configuration options common to all sub-projects/modules.
  
  buildscript {
      repositories {
          jcenter()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:2.3.0'
          classpath 'com.google.gms:google-services:4.0.0'
          // NOTE: Do not place your application dependencies here; they belong
          // in the individual module build.gradle files
      }
  }
  
  allprojects {
      repositories {
          jcenter()
      }
  }
  
  task clean(type: Delete) {
      delete rootProject.buildDir
  }
  </code></pre>