browserify vs bpkg

[nodech]

I noticed there's small difference with browserify vs bpkg backends.
bpkg correctly translate main using browser mappings where browserify
does not translate it using browser mappings.

command: ./node_modules/.bin/bmocha --open -m "$BMOCHA_CHROME" test/*-test.js

e.g.
package.json of the library being used.

{
  "name": "test",
  "main": "./lib/test.js",
  "browser": {
    "./lib/test": "./lib/test-browser.js"
  }
}

This will fail(wont resolve to browser) with browserify backend:

const lib = require('test');

but following will work on both:

const lib = require('test/lib/test');