Typo fix

I think you meant to say $HOME

Author: Spellchaser

en/01.1.md

@@ -119,7 +119,7 @@ sudo tar -xzf go1.8.3.linux-amd64.tar.gz -C /usr/local
 export GOROOT=/usr/local/go
 export GOBIN=$GOROOT/bin
 export PATH=$PATH:$GOBIN
-export GOPATH=HOME/gopath 
+export GOPATH=$HOME/gopath 
 ```    
 Starting from go 1.8, The GOPATH environment variable now has a default value if it is unset. It defaults to $HOME/go on Unix and %USERPROFILE%/go on Windows.
 ### Homebrew