Fixed Gopath problem and wrong folder in Caddy install guide

[theel0ja]

user@server:~/go/src$ cd $GOPATH/src/go/src/github.com/mholt/caddy
-bash: cd: /home/user/go/src/go/src/github.com/mholt/caddy: No such file or directory

[theel0ja]

The right folder found also here: https://github.com/mholt/caddy/wiki/Plugging-in-Plugins-Yourself

[Guaris]

Isn't this the path?
https://github.com/mholt/caddy/tree/master/caddy

[leslitagordita]

Hello @theel0ja, I do not have access to your fork, so I have submitted a PR with your original commits, rebased onto develop and added one additional change: #2212. Thank you for your contribution.