Add a unittest to check the license.md file date range

[thinkingserious]

The end year in the license file should be "this year" and this should be checked on every run of the tests. If the end year is no correct, fail the test.
example:

Copyright (c) 2012-2016 SendGrid, Inc.
It is 2017, so this should be:
Copyright (c) 2012-2017 SendGrid, Inc.
and the test should fail.
--done

[nishithshah2211]

Hey, I'd like to work on this. I am already working on the same issue in the smtpapi-python repo. Should I go ahead with using regex to parse for the year or does anyone want to suggest a better way to do it?

Also, the license file is license.txt and not license.md right?