(ErlangError) Erlang error: "Graphvix.Graph Graphvix.Graph received unexpected message in handle_info/2: :save_state\n"

### Environment

* opus version: 0.5.3
* Elixir / Hex version (mix hex.info): 1.8
* Operating system: MacOS

### Current behavior
When running my app I get the error above. My mix env: 
```
{:opus, "~> 0.5.3"},
{:opus_graph, "~> 0.1", only: [:dev]},
```
