script, lib/discover: Fixup copyright checks

script/check-copyright.go

@@ -29,6 +29,7 @@ var copyrightRegexps = []string{
 	`Copyright`,
 	`package auto`,
 	`automatically generated by genxdr`,
+	`generated by protoc`,
 }
 
 var copyrightRe = regexp.MustCompile(strings.Join(copyrightRegexps, "|"))