Can't swtich language dynamically

The `locale` and `custom-locale` props are not monitored (watched)

This limitation can be bypassed by setting the `key` attribute.
```vue
<template>
  <cron-light :locale="mylocale" :key="mylocale" />
<template>
```
This will force `vue` to create a new instance of the component everytime `mylocale` is changed.