Changed variable name to better reflect value

Calling the variable that holds the deserialized record or array of records `primary` is confusing because it's suggestive (in the case of DB records or JSON representations thereof) of primary keys.

The method signatures for `_addRecordsToCache` and `_addRecordToCache` use `records` and `record`, respectively, so this is consistent with their use.
Merge pull request #38 from jordansexton/patch-1

Changed variable name to better reflect value