docs(readme): Added lgtm badges

README.md

@@ -2,6 +2,7 @@
 [![build status][travis-image]][travis-url]
 [![coverage status][coverage-image]][coverage-url]
 [![Greenkeeper badge](https://badges.greenkeeper.io/grantila/fetch-h2.svg)](https://greenkeeper.io/)
+[![Language grade: JavaScript][lgtm-image]][lgtm-url]
 
 
 # fetch-h2
@@ -289,3 +290,5 @@ const response = await fetch( url, { method, body } );
 [travis-url]: https://travis-ci.org/grantila/fetch-h2
 [coverage-image]: https://coveralls.io/repos/github/grantila/fetch-h2/badge.svg?branch=master
 [coverage-url]: https://coveralls.io/github/grantila/fetch-h2?branch=master
+[lgtm-image]: https://img.shields.io/lgtm/grade/javascript/g/grantila/fetch-h2.svg?logo=lgtm&logoWidth=18
+[lgtm-url]: https://lgtm.com/projects/g/grantila/fetch-h2/context:javascript