Deprecated Stan syntax needs to be updated

[andrjohns]

Hi,

The Stan syntax in your package will soon be incompatible with an upcoming version of RStan. I attempted to update the syntax for you, but the Stan code in this repository is incorrect and does not compile in its current state (regardless of version).

Please update your Stan models soon to avoid your package being broken by the upcoming update.

More information about the deprecated and removed syntax in Stan can be found here:

• https://mc-stan.org/docs/functions-reference/deprecated-functions.html
• https://mc-stan.org/docs/functions-reference/removed-functions.html