Merge pull request #6 from tolking/dev

chore: add rollup to build

Merge pull request #4 from tolking/dev

- suppert image-set
- fix error on nuxt
- remove v-lazy:background

Merge pull request #3 from tolking/dev

fix dataset is undefined on IE

Merge pull request #2 from tolking/dev

- suppert loading="eager"
- change README