chore: update travis.yml

[atian25]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #17 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #17   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           6      6           
  Lines          18     18           
=====================================
  Hits           18     18

---

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 618b28d...c81f90b. Read the comment docs.