Bump target Go version to 1.20

[nywilken]

What's Changed?

This change bumps the minimum Go version to 1.20 to take advantage of a number of fixes to the language, while supporting the minimum version for a number of key dependencies which have been moving away from Go 1.15.

This change officially removes Go 1.15 from the testing matrix and adds the Go versions used for supporting the Exercism CLI and exercises. Namely Go 1.20.x, and 1.21.x.

Additional Changes

These changes support the Go version bump:

• Update build tags to Go 1.18 syntax
• Replace calls to deprecated io/ioutil pkg
• Add multiple Go versions to testing matrix This change officially removes Go 1.15 from the testing matrix
  and adds the Go versions used for supporting the Exercism CLI.
• Update module github.com/spf13/cobra to v1.7.0
• Update various dependencies from golang.org/x to address reported vulnerabilities.

Critical Dependency Changes:

• bump spf13/viper to address reported vulnerabilities in yaml.v2

~>  govulncheck -test ./...
Scanning your code and 210 packages across 21 dependent modules for known vulnerabilities...

Vulnerability https://github.com/nywilken/exercism-cli/pull/1: GO-2022-0956
    Excessive resource consumption in gopkg.in/yaml.v2
  More info: https://pkg.go.dev/vuln/GO-2022-0956
  Module: gopkg.in/yaml.v2
    Found in: gopkg.in/yaml.v2@v2.0.0-20170721122051-25c4ec802a7d
    Fixed in: gopkg.in/yaml.v2@v2.2.4
    Example traces found:
      https://github.com/nywilken/exercism-cli/pull/1: cmd/submit.go:129:23: cmd.getExerciseSolutionFiles calls viper.Viper.ReadInConfig, which eventually calls yaml.Unmarshal

Vulnerability https://github.com/exercism/cli/issues/2: GO-2021-0061
    Denial of service in gopkg.in/yaml.v2
  More info: https://pkg.go.dev/vuln/GO-2021-0061
  Module: gopkg.in/yaml.v2
    Found in: gopkg.in/yaml.v2@v2.0.0-20170721122051-25c4ec802a7d
    Fixed in: gopkg.in/yaml.v2@v2.2.3
    Example traces found:
      https://github.com/nywilken/exercism-cli/pull/1: cmd/submit.go:129:23: cmd.getExerciseSolutionFiles calls viper.Viper.ReadInConfig, which eventually calls yaml.Unmarshal

Vulnerability https://github.com/exercism/cli/issues/3: GO-2020-0036
    Excessive resource consumption in YAML parsing in gopkg.in/yaml.v2
  More info: https://pkg.go.dev/vuln/GO-2020-0036
  Module: gopkg.in/yaml.v2
    Found in: gopkg.in/yaml.v2@v2.0.0-20170721122051-25c4ec802a7d
    Fixed in: gopkg.in/yaml.v2@v2.2.8
    Example traces found:
      https://github.com/nywilken/exercism-cli/pull/1: cmd/submit.go:129:23: cmd.getExerciseSolutionFiles calls viper.Viper.ReadInConfig, which eventually calls yaml.Unmarshal

---

Closes: #1087
Closes: #1086
Closes: #1085

[github-actions]

Hello. Thanks for opening a PR on Exercism. We are currently in a phase of our journey where we have paused community contributions to allow us to take a breather and redesign our community model. You can learn more in this blog post. As such, all issues and PRs in this repository are being automatically closed.

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[ErikSchierboom]

LGTM @ekingery Could you review the code?

[ekingery]

Looks nice and clean to me! Thanks so much for taking this on, @nywilken. I haven't done an upgrade of this magnitude in the recent past, so I can't offer any specific Go expertise in this area. However the tests are all passing on the updated versions so let's

[ekingery]

@ErikSchierboom I'm not sure how to remove the old checks from 1.15 that still seem to be required on this PR... The new 1.20 and 1.21 checks are all passing. Maybe you can just force merge it?

[ErikSchierboom]

Sure! Thanks @nywilken and @ekingery