fix branch name in coveralls links

Author: heldinz

readme.md

@@ -1,6 +1,6 @@
 # [gulp](http://gulpjs.com)-convert-encoding
 [![Build Status](https://travis-ci.org/heldinz/gulp-convert-encoding.svg?branch=master)](https://travis-ci.org/heldinz/gulp-convert-encoding)
-[![Coverage Status](https://coveralls.io/repos/heldinz/gulp-convert-encoding/badge.svg?branch=master)](https://coveralls.io/r/heldinz/gulp-convert-encoding?branch=master)
+[![Coverage Status](https://coveralls.io/repos/heldinz/gulp-convert-encoding/badge.svg?branch=main)](https://coveralls.io/r/heldinz/gulp-convert-encoding?branch=main)
 [![Dependency Status](https://david-dm.org/heldinz/gulp-convert-encoding.svg)](https://david-dm.org/heldinz/gulp-convert-encoding)
 [![NPM Downloads](https://img.shields.io/npm/dm/gulp-convert-encoding.svg)](https://www.npmjs.com/package/gulp-convert-encoding)