build: update `go` directive in `go.mod` to 1.17

[Juneezee]

Runs go mod tidy -go=1.17. This PR updates the go version in go.mod to 1.17 to match the minimum supported Go version in CircleCI and Dockerfiles.

Reference: https://github.com/cossacklabs/acra/pull/558

Checklist

• [x] Change is covered by automated tests
• [x] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [x] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)