Apply exit code to hadolint.sh

[paulbarton90]

Exiting with an exit code of 1 marks the job in github actions as a fail properly. This should help to fix #48. I have noticed that you need to explicitly add docker.io to the trusted registries when running the github action. I updated the testing action to run with the following configuration:

steps:
  - uses: actions/checkout@v2 
  - uses: hadolint/hadolint-action@v1.6.0
    with:
      dockerfile: Dockerfile
      trusted-registries: "docker.io"

[lorenzo]

thanks!

[offa]

Thank you!

[paulbarton90]

No problem. I believe the "trusted-registries" part is also fixed so is not longer required when running in the action.