need ES5 version ready in npm package

[kerryChen95]

front-end developers usually configure bundler, like webpack, not to use babel to compile ES6+ codes inside node_modules directory, otherwise babel need to compile tons of codes and it's too slow.

so I hope node-mine provide ES5 version out from npm package by using package.json browser field to hint bundler which module to use.

[broofa]

The legacy version works with ES5. npm install mime@^1

Documentation for the legacy api can be found here