Enable multi-linter

[dhui]

Is your feature request related to a problem? Please describe. Should enforce a consistent coding style and catch silly errors.

Describe the solution you'd like

• Use a tool (or multiple tools) that should:
  • Enforce a coding style
  • Catch silly errors
  • Integrate with CI (be run on every commit and PR)
  • Run offline (e.g. on dev machine)

Currently, the fastest linter that does all of the above is golangci-lint. As of v1.11, it supports packages/modules.

Describe alternatives you've considered gometalinter - also runs multiple linters in parallel and meets all of the requirements above, but is slower since it doesn't re-use parsed ASTs. See: https://github.com/golangci/golangci-lint#why-golangci-lint-is-faster

Additional context N/A

[dhui]

golangci-lint now runs in TravisCI thanks to @kmuratov !

We still need to enable the following linters:

• [ ] golint
• [ ] dupl
• [x] maligned
• [ ] gosec
• [x] errcheck (undisable)
• [x] staticcheck (undisable)