add coverage.txt to .gitignore

[dmowcomber]

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:

• add coverage.txt to .gitignore

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

[codecov]

Codecov Report

Merging #252 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #252   +/-   ##
=======================================
  Coverage   71.07%   71.07%           
=======================================
  Files           3        3           
  Lines         446      446           
=======================================
  Hits          317      317           
  Misses        125      125           
  Partials        4        4

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[thinkingserious]

Hello @dmowcomber,

Thanks again for the PR!

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

Team SendGrid DX