Updating forecast.io URL

Super cool project!!

I noticed that the URL for forecast.io in the project README 404s when you follow it:
![forecastio](https://cloud.githubusercontent.com/assets/274668/4546053/268e5b12-4e40-11e4-996f-8a54c257e62f.png)

I stuck an "http://" on that URL and it works as advertised.

Thanks for sharing this work!