Switch to SQLite for the Absinthe Tutorial

[kevinastone]

Moving from Postgres to SQLite removes a system dependency and allows one to setup a working environment faster.

[kevinastone]

Hmm, there's hard-coded postgresql in the tutorial:

https://github.com/kevinastone/absinthe_tutorial/blob/master/lib/blog/content/content.ex#L9

[kevinastone]

Updated the where clause to just use date(published_at) == $date