chore: Update LICENSE.txt

[GaryLeutheuser]

This pull request addresses #37.

If the end year isn't supposed to be 2017, let me know what it should be and I'll change it again.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

@GaryLeutheuser

We have not been able to merge your Pull Request, but because you are awesome - we wanted to make sure you could still get a SendGrid Hacktoberfest shirt.

Please go fill out our swag form before Nov 5th and we will send the shirt! (We know that you might have tried this before and it didn’t work, sorry about that!)

You have till Nov 5th to fill out this form in order to get the Hacktoberfest shirt!

Thank you for contributing during Hacktoberfest! We hope to see you in the repos soon! Just so you know, we always give away a SendGrid shirt for your first ever non-Hacktoberfest PR that gets merged.

[thinkingserious]

Hello @GaryLeutheuser,

Thanks again for the PR!

It's HACKTOBERFEST! We want to show our appreciation by sending you some special Hacktoberfest swag. If you have not already, could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX