Update travis config to use relative path

[siburny]

Fixes

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:

This PR fixes hard-coded full path in the travis build file. When someone works with the forked repository, travis builds always fail because of that.

[SendGridDX]

All committers have signed the CLA.

[siburny]

Rebuilding travis

[thinkingserious]

Hello @siburny,

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