chore: add Python 3.8 to Travis

[childish-sambino]

No description provided.

[codecov]

Codecov Report

Merging #140 into master will increase coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #140      +/-   ##
==========================================
+ Coverage   92.95%   93.11%   +0.16%     
==========================================
  Files           6        6              
  Lines         298      305       +7     
==========================================
+ Hits          277      284       +7     
  Misses         21       21              

Impacted Files	Coverage Δ
tests/test_unit.py	99.27% <0.00%> (+0.01%)	⬆️
python_http_client/exceptions.py	97.43% <0.00%> (+0.06%)	⬆️
python_http_client/client.py	81.44% <0.00%> (+0.79%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c05691e...8dff0dd. Read the comment docs.

[thinkingserious]

Hello @childish-sambino,

Thanks again for the PR!

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

Team SendGrid DX