arm64 docker image

Support running the Pacu docker image on arm system (M1 macs)

```bash
$ docker run -it --rm rhinosecuritylabs/pacu:latest
Unable to find image 'rhinosecuritylabs/pacu:latest' locally
latest: Pulling from rhinosecuritylabs/pacu
docker: no matching manifest for linux/arm64/v8 in the manifest list entries
```
