v6 docs: directive usage example wrong
======================================
https://github.com/KABBOUCHI/vue-tippy/blame/c2d6d928706f16e9a961f220a9f71cd20fda10d8/docs/content/en/basic-usage.md#L20-L26
```js
export default {
directives: {
'v-tippy': directive,
},
}
```
should be
```js
export default {
directives: {
tippy: directive,
},
}
```
otherwise you need to use the directive as `v-v-tippy`.