v-popover component isn't globally registered on build (but it is globally registered on dev)

I am globally registering this module

```
import VTooltip from 'v-tooltip'
let tooltipOptions = {
popover: {
defaultPlacement: 'top',
defaultBaseClass: 'vue-tooltip vue-popover',
defaultInnerClass: 'popover-inner'
}
}
Vue.use(VTooltip, tooltipOptions)
```

It works perfectly on dev, but when I run build the error is `Unknown custom element: `

I can import the component individually in my .Vue file by using

`import { VPopover } from 'v-tooltip'`

But this makes it difficult to use any global settings for these components.