Ensure script tags load in order

For each script tag, wait for the external source to be loaded before moving on to the next script tag.

Before:

![screen shot 2014-12-04 at 10 50 49 am](https://cloud.githubusercontent.com/assets/669/5304084/2ee8e412-7ba4-11e4-859e-0ef3874c6f64.png)

After:

![screen shot 2014-12-04 at 10 53 46 am](https://cloud.githubusercontent.com/assets/669/5304086/32db4128-7ba4-11e4-901d-8fe006b6d5e2.png)