Requires nonexistent dependency: github.com/maufl/dhkx

```
../../maufl/dtls/key_agreement.go:4:2: cannot find package "github.com/maufl/dhkx" in any of:
        /usr/local/Cellar/go/1.10.1/libexec/src/github.com/maufl/dhkx (from $GOROOT)
        /Users/nickysemenza/go/src/github.com/maufl/dhkx (from $GOPATH)
```

go get seems to indicate this might be a private repo?