Removing relative directory line on extract_files function in the command line interface

[CatherineH]

This is an attempt to fix #539 . I'm not sure why the relative directory comparison was originally included, hopefully this doesn't break anything. I tested this on the following patterns:

proselint proselint
proselint /home/catherine/python_projects/proselint/proselint
proselint CONTRIBUTING.md
proselint ~/python_projects/proselint/proselint
proselint CONTRIBUTING.md proselint

Everything seemed to work...

[coveralls]

Coverage increased (+0.07%) to 77.817% when pulling 2feca9c on CatherineH:ch-539 into 66a4913 on amperser:master.

[suchow]

Thanks. I tested this out locally and it seems to work well, adding new functionality to the command line that allows it to lint an entire folder from outside the folder. Is that right?

[CatherineH]

Oh, I had assumed that the command line was supposed to be able to lint any folder. Yes, it can now do that.

[suchow]

Thank you!

[mpacer]

Also, if your assumptions result in making Proselint even better than it is, please keep assuming :).

Thank you a tonne!