doc: minor typo fix in README.md

[naftalimurgor]

Summary

1. Minor typo fix from jsbgl.js to jsbgl . The module is published as jsbgl and not jsbgl.js which can be misleading.

Context: doing npm install jsbgl.js throws the following error

[nmurgor@nmurgor src]$  npm install jsbgl.js
npm ERR! code E404
npm ERR! 404 Not Found - GET https://registry.npmjs.org/jsbgl.js - Not found
npm ERR! 404 
npm ERR! 404  'jsbgl.js@latest' is not in the npm registry.
npm ERR! 404 You should bug the author to publish it (or use the name yourself!)
npm ERR! 404 
npm ERR! 404 Note that you can also install from a
npm ERR! 404 tarball, folder, http url, or git url.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/nmurgor/.npm/_logs/2023-03-16T06_41_26_673Z-debug.log