Merge pull request astaxie#823 from appleboy/patch-1

fix GOPATH variable

Author: astaxie

zh/01.1.md

@@ -155,7 +155,7 @@ sudo tar -xzf go1.8.linux-amd64.tar.gz -C /usr/local
 export GOROOT=/usr/local/go
 export GOBIN=$GOROOT/bin
 export PATH=$PATH:$GOBIN
-export GOPATH=HOME/gopath (可选设置)
+export GOPATH=$HOME/gopath (可选设置)
 ```
 或者使用: 
 ```sh 
@@ -166,7 +166,7 @@ sudo vim /etc/profile
 export GOROOT=/usr/local/go
 export GOBIN=$GOROOT/bin
 export PATH=$PATH:$GOBIN
-export GOPATH=HOME/gopath (可选设置)
+export GOPATH=$HOME/gopath (可选设置)
 ```
 
 ### homebrew