新版as中，build.gradle中'compile'指令被换成'implementation'

版本：
```
Android Studio 3.1
Build #AI-173.4670197, built on March 22, 2018
JRE: 1.8.0_152-release-1024-b02 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0
```

编译warning：
```
Configuration 'compile' is obsolete and has been replaced with 'implementation'.
It will be removed at the end of 2018
```