[Android] Plugin with id ‘android-library’ not found

從網路上下載了一個範例，開啟時會顯示這個錯誤：
Plugin with id ‘com.android.application’ not found.

解法：

Add the following code to the top of your build.gradle:

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.1.2'
    }
} 

allprojects {
    repositories {
        jcenter()
    }
}

from:

• http://stackoverflow.com/questions/24795079/error1-0-plugin-with-id-com-android-application-not-found
• http://stackoverflow.com/questions/38761358/error1-0-plugin-com-android-application-not-found
• http://stackoverflow.com/questions/18153739/android-studio-plugin-with-id-android-library-not-found