[TEAM] Add Zhi Chen as a reviewer. (#2040)

CONTRIBUTORS.md

@@ -21,6 +21,7 @@ See the [community structure document](http://docs.tvm.ai/contribute/community.h
 - [Lianmin Zheng](https://github.com/merrymercy) AutoTVM
 
 ## Reviewers
+- [Zhi Chen](https://github.com/zhiics)
 - [Xiaoqiang Dan](https://github.com/xqdan)
 - [Liangfu Chen](https://github.com/liangfu)
 - [Masahiro Masuda](https://github.com/masahi)