Fix 'Simplified Price Bucket' example
Fix 'Simplified Price Bucket' example

Specifically:

- Load Prebid.js async
- Wrap the call to `setPriceGranularity` in the Prebid queue

Addresses https://github.com/prebid/prebid.github.io/issues/253

sonobi/prebid.github.io,prebid/prebid.github.io,prebid/prebid.github.io,sonobi/prebid.github.io,prebid/prebid.github.io,sonobi/prebid.github.io