golangci-lint configuration file

golangci-lint can run all the currently enabled linters, and as far as I
can tell, does it in under 5 seconds as opposed to over 180 seconds
(compare `time make cilint` and `time make lint`).

Some of the linters that are listed in the "enabled" section but
commented out looked like a good idea to me, and fairly low hanging
fruit to fix, but they are not passing at the moment.

All the linters covered in the current Makefile are run.

TODO:
- replace lint target in Makefile with golangci-lint
- remove .github/workflow/errcheck.yml

modules/hibp/widget.go

@@ -68,7 +68,7 @@ func (widget *Widget) content() (string, string, bool) {
 		return title, widget.err.Error(), true
 	}
 
-	title = title + widget.sinceDateForTitle()
+	title += widget.sinceDateForTitle()
 	str := ""
 
 	for _, status := range widget.statuses {