Fixes #67 Add CodeCov support to .travis.yml

[mptap]

Fixes #67

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:

• Added CodeCov support to .travis.yml

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.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b054383). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #68   +/-   ##
=========================================
  Coverage          ?   69.44%           
=========================================
  Files             ?        3           
  Lines             ?      108           
  Branches          ?        0           
=========================================
  Hits              ?       75           
  Misses            ?       33           
  Partials          ?        0

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[thinkingserious]

Hello @mptap,

Thanks again for the PR!

We appreciate your contribution and look forward to continued collaboration. Thanks!

Team SendGrid DX