异常如下：

Error:FAILURE: Build failed with an exception.

* What went wrong:
Could not resolve all files for configuration ':app:debugCompileClasspath'.
> Could not resolve com.google.android.gms:play-services-ads:latest.release.
  Required by:
      project :app
   > Could not resolve com.google.android.gms:play-services-ads:12.0.1.
      > Could not get resource 'https://jcenter.bintray.com/com/google/android/gms/play-services-ads/12.0.1/play-services-ads-12.0.1.pom'.
         > Could not GET 'https://jcenter.bintray.com/com/google/android/gms/play-services-ads/12.0.1/play-services-ads-12.0.1.pom'.
            > Read timed out

* 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.

* Get more help at https://help.gradle.org

BUILD FAILED in 35s

解决方案如下：
在project级别下的build.gradle文件中添加如下代码：

buildscript {

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.1' //这里不用和我一样，和你项目里面的版本一样就行
        classpath 'com.google.gms:google-services:4.0.1'  //这行对谷歌服务库进行依赖

    }
}

allprojects {
    repositories {
        google()
        jcenter()
        mavenCentral ()
        maven {url 'https://dl.bintray.com/jetbrains/anko'} //这是你需要加入的，这个是解决这个问题的关键地方，我就是添加这个maven后不再报上面的错误了
        maven {url "https://maven.google.com"} //谷歌广告
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}