Android 同步渐变时发生Firebase错误

我在同步gradle时出现此错误 我已经在

SDK管理器中安装了
Google repository
和
Google play services
，但是我仍然收到这个错误

Error:Could not find com.google.android.gms:play-services-ads:11.4.0.
Searched in the following locations:
file:/C:/Program Files/Android/Android Studio/gradle/m2repository/com/google/android/gms/play-services-ads/11.4.0/play-services-ads-11.4.0.pom
file:/C:/Program Files/Android/Android Studio/gradle/m2repository/com/google/android/gms/play-services-ads/11.4.0/play-services-ads-11.4.0.jar
https://jcenter.bintray.com/com/google/android/gms/play-services-ads/11.4.0/play-services-ads-11.4.0.pom
https://jcenter.bintray.com/com/google/android/gms/play-services-ads/11.4.0/play-services-ads-11.4.0.jar
Required by:
project :

这是我的Gradle文件：

apply plugin: 'com.android.application'

android {
   compileSdkVersion 26
   buildToolsVersion "26.0.1"
   defaultConfig {
    applicationId "ytstudios.wall.bucket"
    minSdkVersion 21
    targetSdkVersion 26
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
   }
}
compile 'com.android.support:design:26.0.1'
compile 'com.android.support:recyclerview-v7:26.0.1'
compile 'com.android.support:cardview-v7:26.0.1'

compile 'com.google.android.gms:play-services:11.4.0'
compile 'com.google.firebase:firebase-ads:11.4.0'


//Firebase Plugin
apply plugin: 'com.google.gms.google-services'

和类路径：

classpath 'com.google.android.gms:play-services-ads:11.4.0'

已解决：
编译类路径
classpath'com.google.gms:googleservices:3.1.0'
并添加了存储库

maven {
        url "https://maven.google.com" // Google's Maven repository
    }

还汇编
编译'com.google.firebase:firebase core:11.4.0'
在Project Gradle中
您必须编译'com.google.android.gms:play services ads:11.4.0'源代码：不，仍然收到错误您可以共享项目级Gradle文件吗。