update docker image

[terryzwt]

https://hub.docker.com/r/itsthenetwork/nfs-server-alpine/tags
The latest image tag is over 5 years, the alpine & nfs is outdated somehow. May you update the image?

[aminvakil]

You may use https://github.com/aminvakil/docker-alpine-nfs-server.

[janjangao]

can refer newest built image based on current unmerged MRs

https://hub.docker.com/r/janjangao/nfs-server-alpine

add some new features, more details check: #63