Drop Travis CI

[smithdc1]

This is what work over the last few months has been leading towards.

This PR drops Travis CI and provides codecov reports via github actions. This has only recently been made available following the release of github action API.

I've got codecov reports uploading on my own repo see here. Let's see if codecov actually posts the usual comment via the new method.

Finally, whilst I've removed the travis.yml file I'm not sure if further work is needed on Travis' website to turn it off for good.

So... are we ready? 🚀

[codecov-io]

Codecov Report

Merging #1007 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1007   +/-   ##
=======================================
  Coverage   97.06%   97.06%           
=======================================
  Files          24       24           
  Lines        2728     2728           
  Branches      241      241           
=======================================
  Hits         2648     2648           
  Misses         39       39           
  Partials       41       41           

Flag	Coverage Δ
#unittests	97.06% <ø> (?)

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[smithdc1]

Awesome codecov responded as normal 👍

[carltongibson]

Come on, let's give it a go. Nice work @smithdc1.