Switch to the standard errors API, that was introduced in 1.13 (#273)

* Switch to the standard errors API, that was introduced in 1.13

* Fix linter errors 🤦‍

* Remove withStackError

* fix: freeze go version to 1.17, since 1.18 introduced generics, which are not supported by linters yet

* fix: freeze go version to 1.17, since 1.18 introduced generics, which are not supported by linters yet

kong.go

@@ -1,6 +1,7 @@
 package kong
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -378,13 +379,14 @@ func (k *Kong) FatalIfErrorf(err error, args ...interface{}) {
 		msg = fmt.Sprintf(args[0].(string), args[1:]...) + ": " + err.Error()
 	}
 	// Maybe display usage information.
-	if err, ok := err.(*ParseError); ok {
+	var parseErr *ParseError
+	if errors.As(err, &parseErr) {
 		switch k.usageOnError {
 		case fullUsage:
-			_ = k.help(k.helpOptions, err.Context)
+			_ = k.help(k.helpOptions, parseErr.Context)
 			fmt.Fprintln(k.Stdout)
 		case shortUsage:
-			_ = k.shortHelp(k.helpOptions, err.Context)
+			_ = k.shortHelp(k.helpOptions, parseErr.Context)
 			fmt.Fprintln(k.Stdout)
 		}
 	}