Make a docker image reference the .nvmrc version

[falgon]

Improvements to use nvmrc have been made in #153, but are currently fixed to use node version 14 for docker image creation. i.e.

roki-web/docker/contents/Dockerfile

Line 37 in 860ccc6

&& curl -sSL https://deb.nodesource.com/setup_14.x | bash \

It needs to be improved to refer to .nvmrc even when creating a docker image, but I do not use it so much, so it may not be necessary to take immediate action.

[falgon]

Articles that may be helpful: https://zenn.dev/uttk/articles/a7b085c7774ae9

[falgon]

#305

[falgon]

#315