catch crashes parsin JSON

```
SyntaxError: Unexpected token F in JSON at position 0
    at JSON.parse (<anonymous>)
    at Request._callback (/node_modules/forecast.io/index.js:79:19)
```
I guess thats from 403 or something, but the app crashes.

Can you put try catch in JSON.parse so it doesnt crash the app.
There is a fix from @danschumann in a pull request or you can just copy paste that 3 lines