加快AndroidStudio gradle编译速度

修改build.gradle
添加阿里云maven仓库

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