Only load default plugins when necessary

[smergler]

General Information

This is for a fix to issue #3.

We only load the default plugins when necessary.

Testing

For testing I was able to run the config discussed in the issue and received the following result:

I had also tried to run it with the problematic argument and received an expected error.

Side note

Admittedly this is not best practice in terms of style, which would require having the imports at the top of the file. However, this is required due to the way that dotbot imports it's plugins.