fix subpackages imports

Fix go app get error:

```
➜  ~GOPATH  goapp get -d  github.com/mjibson/goread
package atom: unrecognized import path "atom"
package rdf: unrecognized import path "rdf"
package rss: unrecognized import path "rss"
package sanitizer: unrecognized import path "sanitiser"
```