Fix search includes

This patch changes the format of the random suffix to the rank column, added in tenderlove/texticle@2d5fc5c19e3ee4e106f5b8f1f4f47018556c2274.

I was also experiencing the issue @GRoguelon mentioned in #3, and it definitely was caused by having includes in my query. After a bit of toying with it, it appears that the random suffix was the issue, more specifically the fact that the number generated by `rand` ended up having a decimal in it, which looks like the notation for "table.column". I'm still not 100% sure whether it was postgres or activerecord choking on that decimal, but replacing it with a short hash from SecureRandom seems to do the trick.

Cheers!