Fix "error margin" on Endpoint::search()

[igorsantos07]

For some odd reason, the ProsperWorks API is not reliable in regards to the number of records returned on search calls. Thus, there's a hacky code that tries to get as much as possible, with a safe margin to allow us to retrieve all paged records.

We should talk with the ProsperWorks Support team about that, get it fixed somehow, and update Endpoint::search().