improved errors.Is implementation

error.go

@@ -75,6 +75,11 @@ func (e *Error) Is(target error) bool {
 		return tErr.tmpl == e.tmpl
 	}
 
+	// target is the template itself, therefore they are considered equal to another
+	if tTmpl, ok := target.(*ErrTmpl); ok {
+		return tTmpl == e.tmpl
+	}
+
 	return false
 }