Could not find com.android.tools.build:gradle:2.3.1

之前：

buildscript {
    repositories {
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.1'
    }
}

allprojects {
    repositories {
        jcenter()
        mavenCentral()
    }
}

之后：

buildscript {
    repositories {
        maven { url 'http://maven.aliyun.com/nexus/content/repositories/google' }
        maven { url 'http://maven.aliyun.com/nexus/content/repositories/jcenter'}
        maven { url 'http://maven.aliyun.com/nexus/content/groups/public/' }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.1'
    }
}

allprojects {
    repositories {
        maven { url 'http://maven.aliyun.com/nexus/content/repositories/google' }
        maven { url 'http://maven.aliyun.com/nexus/content/repositories/jcenter'}
        maven { url 'http://maven.aliyun.com/nexus/content/groups/public/' }
    }
}

原因：

1.jcenter：已经不在停服了，不再提供服务了

2.google在中国被墙了