Don't split module names in Ecto instruments

[cschneid]

This now creates a 2 element list that looks like: [:"myapp/repo", :query] as the Telemetry handler mapping.

Fixes #76

[cschneid]

After reading docs some more, this is incorrect. We need to have the repo naming the way it was.

https://github.com/elixir-ecto/ecto/blob/454bd594637c0b45ed9dc7bb66702863236620be/lib/ecto/repo.ex#L92-L118