gradle 构建项目时因为 jcenter()网络环境不好，经常连接超时。所以改成阿里云镜像来拉取资源构建项目。

需要修改的元素：

1. buildscript  下的 repositories

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

}

2. allprojects下的repositories

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

buildscript {
    
    repositories {
//        google()
//        jcenter()
        maven{ url 'http://maven.aliyun.com/nexus/content/groups/public/' }
        maven{ url 'http://maven.aliyun.com/nexus/content/repositories/jcenter'}
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
        classpath 'com.jakewharton:butterknife-gradle-plugin:8.4.0'
        classpath "com.tencent.tinker:tinker-patch-gradle-plugin:${TINKER_VERSION}"
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

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

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