Use prisma/migrations path for migrations script

[jennmueng]

Fixes #34

The prisma command generates the migration files in the prisma/migrations path not migrations

[akodkod]

I ran into the same issue and spent a few hours trying to figure out why my migrations weren't applying.

Thank you so much for saving me time, @jennmueng! 🙏

P.S. We might need to update the README or script to support multiple possible locations