Upgrade node-sass module to v6.0+

[phyninja]

I installed NodeJS v.16.13.0 on a Linux machine and attempted to build the DShop source code with the command yarn install. The build failed with the following error related to the node-sass module v5.0.0:
error: 'remove_cv_t' is not a member of 'std'
The detailed log is similar to the one posted here: sass/node-sass#3077 (comment)

node-sass' documentation recommends using v6.0+ of their project to work with Node 16. Node 16 is listed under the category of Long Term Support (LTS) as of this writing.