Install Babel Minify, add to presets

[evanmwillhite]

Adds JS minification using https://github.com/babel/minify. Solves #63

To test:

• Clone a fresh copy of Emulsify
• composer install
• Change line 6 in package.json to "emulsify-gulp": "fourkitchens/emulsify-gulp#babel-minify",
• yarn install
• yarn start
• Verify start command runs without errors
• Verify Pattern Lab components with JavaScript work OK
• Verify dist JS is minified. The file here dist/02-molecules/menus/main-menu/main-menu.js should look like code below:

'use strict';(function(){'use strict';var a=document.getElementById('toggle-expand'),b=document.getElementById('main-nav'),c=b.getElementsByClassName('expand-sub');console.log(a),a.addEventListener('click',function(){a.classList.toggle('toggle-expand--open'),b.classList.toggle('main-nav--open')});for(var d=0;d<c.length;d++)c[d].addEventListener('click',function(a){var b=a.currentTarget,c=b.nextElementSibling;b.classList.toggle('expand-sub--open'),c.classList.toggle('main-menu--sub-open')})})();
//# sourceMappingURL=main-menu.js.map