Fix Vue 3 compatability

[unknownCoderDetected]

Hello,

we are using this library in our project, which is being transferred to Vue 3. With this library we ran into some issues.

Firstly, we were getting following error message.

An unexpected error occurred: "expected hoisted manifest for \"vue3-datepicker#vue#@vue/server-renderer#@vue/compiler-ssr\"".

And we have fixed this by upgrading the Vue dependency.

Another issue is the wrong Vue 3 syntax in the watcher, which deals with an attribute value while the watcher should be on modelValue.

Thank you for your time.