Make sure LICENSE file test works cross-platform

[adlan]

Fixes #51

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• Use Path.Combine method instead of hard-coding platform-specific
  path separator because Travis is run on a non-windows platform

If you have questions, please send an email to Sendgrid, or file a Github Issue in this repository.

[SendGridDX]

All committers have signed the CLA.

[adlan]

Also, note that, this PR partially fix the failing Travis build. There are 2 more failing test, I'll see if I can fix those

[mbernier]

@adlan you rock!! Thank you!!

[thinkingserious]

Hello @adlan,

Thanks again for the PR!

We want to show our appreciation by sending you some swag. Could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX

[mbernier]

@adlan
If you are interested, we would love the opportunity to talk to you about Hacktoberfest and our API libraries.

Our agenda would be: Explore what you liked and is there anything we can do to improve?

You can grab a time on my calendar that works for you and we can have a chat on Google Hangout or Skype. If you prefer, you can email me using my GitHub username at my company’s domain.

Thank you so much,

Matt Bernier - @mbernier - SendGrid Developer Experience Product Manager
Elmer Thomas - @thinkingserious - SendGrid Developer Experience Engineer
@sendgrid