Not compatible with Jest ESM

[jasperlin451]

Describe the bug

When trying to upgrade my project to be fully ESM, I run into

    SyntaxError: The requested module '@fortawesome/react-fontawesome' does not provide an export named 'FontAwesomeIcon'

This should be fixable by updating the following lines:

react-fontawesome/package.json

Lines 5 to 7 in 976c1ad

	"main": "index.js",
	"module": "index.es.js",
	"jsnext:main": "index.es.js",

to use the modern Node.js packaging standard.

{
  "type": "module",
  "exports": {
    "import": "./index.es.js",
    "require": "./index.js"
  }
} 

[dhwang]

@jasperlin451 Maybe create a PR for "This should be fixable by updating the following lines:" ?