Add spin.js as dependency in package.json

[Rafael Bodill]

Something like this:

"dependencies": {
  "spin": "~1.3.0"
},
"volo": {
  "url": "https://raw.github.com/hakimel/Ladda/{version}/js/ladda.js",
  "dependencies": {
    "spin": "fgnass/spin.js/~1.3"
  }
},

[Theodore Brown]

spin.js is listed as a dependency in package.json, so I don't think this issue is relevant anymore.