Fix README file typo

There was a very small typo in the README file that I noticed and thought it would be good to update. 
The file reads:
```
It's possible to get around this will jsonp...
```
When it should read:
```
It's possible to get around this with jsonp...
```
Here is a screenshot of the typo:
![screen shot 2014-07-19 at 7 00 00 pm](https://cloud.githubusercontent.com/assets/6327569/3636315/b68fc8a8-0fb2-11e4-86c6-62456339b6ca.png)

Thanks so much for a great product! I am just starting to use it.