Change README `go get` path to prevent error (#55)
Change README `go get` path to prevent error (#55)

Change `go get path` in README to prevent error message:
> package github.com/letsencrypt/pebble: no Go files in $GOPATH/src/github.com/letsencrypt/pebble

shred/pebble,shred/pebble,letsencrypt/pebble,letsencrypt/pebble,letsencrypt/pebble