*: Dockfile upgrade to golang:1.9 (#4717)
*: Dockfile upgrade to golang:1.9 (#4717)

See https://github.com/pingcap/tidb/pull/4527 Bumping golang version to 1.9.
kyle-wang/tidb,pingcap/tidb,ngaut/tidb,pingcap/tidb,Nify/tidb,yuanwhy/tidb,zimulala/tidb,yangwenmai/tidb,ngaut/tidb,cosmtrek/tidb,c4pt0r/tidb,mccxj/tidb,ngaut/tidb,ngaut/tidb,CodeRushing/tidb,pingcap/tidb,EvilMcJerkface/tidb,CodeRushing/tidb,yuanwhy/tidb,kyle-wang/tidb,c4pt0r/tidb,8cbx/tidb,c4pt0r/tidb,c4pt0r/tidb,Cofyc/tidb,kyle-wang/tidb,Cofyc/tidb,cosmtrek/tidb,mccxj/tidb,yangwenmai/tidb,pingcap/tidb,pingcap/tidb,spongedu/tidb,kyle-wang/tidb,ngaut/tidb,wusphinx/tidb,tiancaiamao/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,qiuyesuifeng/tidb,XuHuaiyu/tidb,Nify/tidb,c4pt0r/tidb,ming-relax/tidb,coocood/tidb,spongedu/tidb,tiancaiamao/tidb,ming-relax/tidb,pingcap/tidb,wusphinx/tidb,ngaut/tidb,kyle-wang/tidb,8cbx/tidb,kyle-wang/tidb,XuHuaiyu/tidb,qiuyesuifeng/tidb,zimulala/tidb,coocood/tidb