batch_get bug fix

This release fixes a bug where batch_get queries for lists of interpolated values was failing. Queries in both of the following formats will now work...

Repo.all(from m in Model, where: m.id in ["id_1", "id_2"])

# or...

model_ids = ["id_1", "id_2"]
Repo.all(from m in Model, where: m.id in ^model_ids)