Change errors to use xerrors package.

config/errors.go

@@ -1,14 +0,0 @@
-package config
-
-import "fmt"
-
-// ValidationError represents a config validation error
-type ValidationError struct {
-	Param  string
-	Value  string
-	Reason string
-}
-
-func (e ValidationError) Error() string {
-	return fmt.Sprintf("invalid value '%s' for %s: %s", e.Value, e.Param, e.Reason)
-}