build(ci): test matrix include go1.12 up to go1.18

[mroth]

This tests back from the version specified in go.mod to current stable.

This should enable detection of any breaking version changes as part of the dependencies update PR.

subtask forked from #28.

[codecov-commenter]

Codecov Report

Merging #30 (f253a4f) into master (e9f389d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #30   +/-   ##
=======================================
  Coverage   79.47%   79.47%           
=======================================
  Files           5        5           
  Lines         268      268           
=======================================
  Hits          213      213           
  Misses         38       38           
  Partials       17       17           

---

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[mroth]

There appears to be a tooling issue with the version of golangci-lint here working with go1.18. As a first attempt before spelunking all of the golangci-lint changelogs, I'm going to just update the version of golangci-lint to latest stable and see if that fixes things without causing any issues (it appears from the config file not many linters are being run).

[lestrrat]

Thanks, as for golangci-lint, I'm going to refactor it out to its own job after merging this.