chore: using node version 13 in github workflow

[pedroferreira1]

Motivation

After the release of v0.10.0 we had a problem with the deploy of the explorer version. https://github.com/HathorNetwork/hathor-explorer/runs/4432263445?check_suite_focus=true

> hathor-admin@0.10.0 build-css
> node-sass-chokidar src/ -o src/

/home/runner/work/hathor-explorer/hathor-explorer/node_modules/node-sass/lib/binding.js:13
      throw new Error(errors.unsupportedEnvironment());
      ^

Error: Node Sass does not yet support your current environment: Linux 64-bit with Unsupported runtime (93)
For more information on which environments are supported please see:
https://github.com/sass/node-sass/releases/tag/v4.13.1
    at module.exports (/home/runner/work/hathor-explorer/hathor-explorer/node_modules/node-sass/lib/binding.js:13:13)
    at Object.<anonymous> (/home/runner/work/hathor-explorer/hathor-explorer/node_modules/node-sass/lib/index.js:14:35)
    at Module._compile (node:internal/modules/cjs/loader:1101:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Module.require (node:internal/modules/cjs/loader:1005:19)
    at require (node:internal/modules/cjs/helpers:102:18)
    at Object.<anonymous> (/home/runner/work/hathor-explorer/hathor-explorer/node_modules/node-sass-chokidar/bin/node-sass-chokidar:18:9)
    at Module._compile (node:internal/modules/cjs/loader:1101:14)
ERROR: "build-css" exited with 1.
make: *** [Makefile:26: mainnet_build] Error 1
Error: Process completed with exit code 2.

The node-sass package could not be installed and the link with supported versions (https://github.com/sass/node-sass/releases/tag/v4.13.1) shows that this package does not support node 14

[r4mmer]

The node-sass repo starts with a warning

Warning: LibSass and Node Sass are deprecated.
While they will continue to receive maintenance releases indefinitely, there are no plans to add additional features or compatibility with any new CSS or Sass features.
Projects that still use it should move onto Dart Sass.

Should we start moving to Dart Sass?

[luislhl]

Maybe we should use version 12 instead of 13, because 13 is not supported anymore: https://nodejs.org/en/about/releases/

12 will be supported until april 2022.

In the meatime, I think we should do what r4mmer suggested, so we are able to move to newer Node.js versions in the future.

[pedroferreira1]

Makes sense. Changed here: 2959467 and created an issue because of @r4mmer suggestion (#145)

[pedroferreira1]

The node-sass repo starts with a warning

Warning: LibSass and Node Sass are deprecated.
While they will continue to receive maintenance releases indefinitely, there are no plans to add additional features or compatibility with any new CSS or Sass features.
Projects that still use it should move onto Dart Sass.

Should we start moving to Dart Sass?

Created an issue to handle this in the future: #145