Component name doesn't forrow Vue Style Guide

[zakuro9715]

https://vuejs.org/v2/style-guide/#Multi-word-component-names-essential

Multi word component name is Essential.

This library uses one word components likes <drag>. But we should use multi word likes <vue-drag>

I purpose to add alias to current components as first step.

[theoc1]

import { Drag as VueDrag, Drop as VueDrop } from 'vue-drag-drop';

export default {
  components: { VueDrag, VueDrop },
};