* Update golangci-lint
To accomodate the recent Go 1.18 upgrade
* Fix new lint warnings as a result of linter upgrade
* Set golangci-lint to Go 1.18 mode
golangci-lint will automatically skip linters that don't have support
for Go 1.18.
See: https://github.com/golangci/golangci-lint/issues/2649
- Don't assume an explicit $GOPATH is set
- Remove golint from linters - it's been deprecated for over a year
and golangci-lint prints a warning instead of running it.