Add vue extension when importing components

[JuanKman94]

When working with Vue 3 with Vite instead of webpack, one can import the components from source but it breaks because the imports don't include the file extension.

With these changes, one can:

<template>
  ...
</template>

<script>
import VSwatches from 'vue-swatches/src/VSwatches.vue'

...
</script>

And use the swatches