removes markdown code markers from displaying in the active record querying guide

Removes code markers (```ruby) which render in the generated Active Record Querying guide as seen below.

![screen shot 2013-07-04 at 8 32 58 pm](https://f.cloud.github.com/assets/155215/751646/750ddad8-e50a-11e2-9993-38b14616d72b.png)