chore: add Python 3.8 to Travis

[childish-sambino]

No description provided.

[codecov]

Codecov Report

Merging #870 into master will decrease coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #870      +/-   ##
==========================================
- Coverage   79.92%   79.67%   -0.25%     
==========================================
  Files          70       70              
  Lines        2017     2017              
  Branches      338      338              
==========================================
- Hits         1612     1607       -5     
- Misses        206      210       +4     
- Partials      199      200       +1

Impacted Files	Coverage Δ
sendgrid/helpers/mail/email.py	86.41% <0%> (-6.18%)	⬇️

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[thinkingserious]

Hello @childish-sambino,

Thanks again for the PR!

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

Team SendGrid DX