Sanctuary's short configuration option (-c) raises ConfigurationNotFound error

👓 What did you see?

Passing a short configuration option to sanctuary (-c=.logan.yaml) raises a ConfigurationNotFound error.

sanctuary also logs Could not find configuration file "=.logan.yaml" (note the leading equals sign)

✅ What did you expect to see?

sanctuary operating on the secrets defined in the configuration file passed as a short configuration option.

💻 Where does this happen?

When using sanctuary in the command line.

🔬 How do I recreate this?

1. Invoke any sanctuary command with a short configuration option and an equals sign eg. -c=.logan.yaml

📚 Any additional information?

This does not happen with the long option eg. --configuration=.logan.yaml, which works as expected.

It also does not happen when the short option is used without an equals sign eg. -c .logan.yaml.
However, the sanctuary spec uses the equals sign: -c=FILE (logan/sanctuary/tool.py#L12)

I believe this is related to this open issue in docopt: Usage of short options with argument keeps unneeded equal sign #331