go.blog: small fixes to slices article
go.blog: small fixes to slices article

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/8402043

webfd/go-zh.blog,bryanxu/go-zh.blog,bryanxu/go-zh.blog,d0f/go-zh.blog,webfd/go-zh.blog,d0f/go-zh.blog