Fix up another unix-path-ism

[Yasumoto]

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PR Summary

This change allows the RtmBot to successfully find plugins in the current directory.

Related Issues

Last piece related to #59

Test strategy

Ran RtmBot on a Windows laptop

[coveralls]

Coverage remained the same at 34.194% when pulling d384c8f on yasumoto-final-windows-fix into a9bf314 on master.

[coveralls]

Coverage remained the same at 34.194% when pulling d384c8f on yasumoto-final-windows-fix into a9bf314 on master.