test: add CodeCov support to .travis.yml

[mptap]

Fixes #55

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 Add CodeCov support to .travis.yml #55

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[SendGridDX]

All committers have signed the CLA.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@42c22d2). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             main       #56   +/-   ##
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  Coverage        ?   100.00%           
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  Files           ?         1           
  Lines           ?        84           
  Branches        ?         0           
========================================
  Hits            ?        84           
  Misses          ?         0           
  Partials        ?         0           

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