解决Unknown host ‘jcenter.bintray.com‘问题

使用开源中国的maven库：

阿里云的：http://maven.aliyun.com/nexus/content/groups/public/

在项目根目录下的build.gradle中添加如下：

buildscript {

    repositories {
        maven{url 'http://maven.aliyun.com/nexus/content/groups/public/'}
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.2'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

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

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