Fix Travis CI links

[hugovk]

https://travis-ci.com/ultrajson/ultrajson -> https://app.travis-ci.com/github/ultrajson/ultrajson

Looks like Travis has retired the former without putting in redirects 🤷

[codecov-commenter]

Codecov Report

Merging #540 (f1e62b8) into main (80d0bd4) will not change coverage.
The diff coverage is n/a.

❗ Current head f1e62b8 differs from pull request most recent head 9e82032. Consider uploading reports for the commit 9e82032 to get more accurate results

@@           Coverage Diff           @@
##             main     #540   +/-   ##
=======================================
  Coverage   91.76%   91.76%           
=======================================
  Files           6        6           
  Lines        1821     1821           
=======================================
  Hits         1671     1671           
  Misses        150      150           

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