ref from:
Android Studio下“Error:Could not find com.android.tools.build:gradle:2.2.1”的解决方法
http://blog.csdn.net/klovesq/article/details/45576635
错误：
Error:Could not find com.android.tools.build:gradle:2.2.1.
Searched in the following locations:
file:/D:/Program Files/Android/android-studio/gradle/m2repository/com/android/tools/build/gradle/2.2.1/gradle-2.2.1.pom
file:/D:/Program Files/Android/android-studio/gradle/m2repository/com/android/tools/build/gradle/2.2.1/gradle-2.2.1.jar
https://jcenter.bintray.com/com/android/tools/build/gradle/2.2.1/gradle-2.2.1.pom
https://jcenter.bintray.com/com/android/tools/build/gradle/2.2.1/gradle-2.2.1.jar
后来尝试后找到的解决方法为：
1、进入file:/D:/Program Files/Android/android-studio/gradle/m2repository/com/android/tools/build/gradle/，查看当前已有内容如下
2、于是在build.gradle中做如下修改
3、sync后解决。
附：
gradle plugin version for as 3.0 beta2:
gradle plugin version for as 2.3.3:
build tools version:
