Add optional drive prefix to support windows

Add drive prefix to regex to fix issue (https://github.com/btm/minitest-handler-cookbook/issues/60) on windows where it was unable to find tests as the convert-full-file-path-to-relatative-path functionality was failing.
spec test to illustrate #60
Merge branch 'master' of https://github.com/matt-richardson/minitest-handler-cookbook into matt-richardson-master
rubocop cleanup and change spec dir layout
rubocop cleanup and change spec dir layout
Merge branch 'matt-richardson-master'