message: Added maintained badge
diff: ## Status
  [![Build Status](https://travis-ci.org/zxing-js/library.svg?branch=master)](https://travis-ci.org/zxing-js/library)
  -![Dependencies](https://david-dm.org/zxing-js/library.svg)
  +[![Maintainer wanted](https://img.shields.io/badge/maintained-help%20wanted-red)](https://npmjs.org/package/@zxing/ngx-scanner)
  [![Greenkeeper badge](https://badges.greenkeeper.io/zxing-js/library.svg)](https://greenkeeper.io/)
  [![NPM version](https://img.shields.io/npm/v/@zxing/library.svg?&label=npm)][0]
  [![Contributors](https://img.shields.io/github/contributors/zxing-js/library.svg)](https://github.com/zxing-js/library/graphs/contributors)
  [![Commits to deploy](https://img.shields.io/github/commits-since/zxing-js/library/master.svg?label=commits%20to%20deploy)](https://github.com/zxing-js/library/compare/master...develop)
  -[![Codacy Badge](https://api.codacy.com/project/badge/Grade/9aaa5317fcc740af9f25b3c7f832aa1d)](https://www.codacy.com/app/zxing/library?utm_source=github.com&amp;utm_medium=referral&amp;utm_content=zxing-js/library&amp;utm_campaign=Badge_Grade)
  [![Maintainability](https://api.codeclimate.com/v1/badges/2b9c6ae92412ee8e15a9/maintainability)](https://codeclimate.com/github/zxing-js/library/maintainability)
  [![Test Coverage](https://api.codeclimate.com/v1/badges/2b9c6ae92412ee8e15a9/test_coverage)](https://codeclimate.com/github/zxing-js/library/test_coverage)
  [![BCH compliance](https://bettercodehub.com/edge/badge/zxing-js/library?branch=master)](https://bettercodehub.com/)
  