Fix incorrect "node-browserify" dev dependency

The module is just called "browserify", not "node-browserify". An `npm install`
in this repo fails because of this difference, since a tarball containing a
module called "browserify" is downloaded yet `npm` is expecting one containing
a "node-browserify" module.

    $ npm install
    npm ERR! Error: Invalid Package: expected node-browserify but found browserify

I guess no one has tried running `npm install` here until today: npm/npm#6202
Merge pull request #7 from KenanY/fix-browserify

Fix incorrect "node-browserify" dev dependency