Update dependencies and support running in browser

[kinland]

This PR does two things:

• update dependencies with npm audit fix --force
• conditionally polyfill Buffer, Crypto, and Constants. A Node.js project should thus be unaffected by these changes, but browser users can now use node-rsa out of the box without having to do polyfilling themselves.

This includes changes from @learntheropes 's fork for running node-rsa in the browser out of the box. The main thing their fork does is use the buffer package instead of assuming Buffer was available. Their fork did not make this a conditional change, which means someone using @learntheropes/node-rsa in node will end up using the npm package rather than the node one. My changes address this.

[rzcoder]

Works in browser out of the box via conditional polyfills

sounds too strong considering that using it in the browser still requires bundling