Updating lookup_by :http_method

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![image](https://cloud.githubusercontent.com/assets/1637481/3359808/76ebe02c-faec-11e3-93de-4f0bcda6efa0.png)

I noticed all the other ```lookup_by``` methods have the cache set to an actual number.  After doing some digging into ```lookup_by```, I found [this](https://github.com/companygardener/lookup_by/commit/b90c46b09c02b5d94673c662bbd3cf44b07e3d1d).