Update Cart in Nav with Cart Size

### Description

When a user adds a product to their cart, the cart size in the nav is not updating.

### How To Reproduce

1. Run the App Locally
2. Add item to cart
3. See that cart in nav says 0

https://user-images.githubusercontent.com/2349518/166160150-c3c78481-6338-4ed4-9742-f1f71deb40a3.mov

### Deliverables

- [ ] Link the cart size to the nav
