chore(deps): Update tailwind to 2.1 to natively support JIT

[RomainMazB]

Hi there!

TailwindCSS team added the JIT mode to the core!

Some issues could probably resolve itself if we stop using the additional jit true/false config and let the process be more fluid #299, #298, #302 .

Since the JIT mode needs "a basic" purge config for now (an array referring files to watch instead of a object containing a content property), I also updated the documentation to make it clear that we need to override the default nuxtjs-tailwind purge config from this:

export default ({ _dev, rootDir, srcDir }) => ({
  purge: {
    content: [
      `${srcDir}/components/**/*.{vue,js}`,
      `${srcDir}/layouts/**/*.vue`,
      `${srcDir}/pages/**/*.vue`,
      `${srcDir}/plugins/**/*.{js,ts}`,
      `${rootDir}/nuxt.config.{js,ts}`
    ],
    // https://tailwindcss.com/docs/optimizing-for-production#purge-css-options
    options: {}
  }

to this:

export default {
  mode: 'jit',
  purge: [
    `~/components/**/*.{vue,js}`,
    `~/layouts/**/*.vue`,
    `~/pages/**/*.vue`,
    `~/plugins/**/*.{js,ts}`,
    `~~/nuxt.config.{js,ts}`
  ]
}

I would like to add some test for this, but I'm not so comfortable with Jest to analyze the javascript compilated file to expect the top-[12px] class to be present in it.

[codecov]

Codecov Report

Merging #326 (e76f0f2) into main (42c23c8) will not change coverage.
The diff coverage is 100.00%.

❗ Current head e76f0f2 differs from pull request most recent head 93fda82. Consider uploading reports for the commit 93fda82 to get more accurate results

@@            Coverage Diff            @@
##              main      #326   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           37        41    +4     
  Branches         8         9    +1     
=========================================
+ Hits            37        41    +4     

Impacted Files	Coverage Δ
src/index.ts	100.00% <100.00%> (ø)
src/tailwind.config.ts	100.00% <100.00%> (ø)

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[viennv1709]

Update src\index.ts to reflect changes

[RomainMazB]

@atinux
Why this isn't merged yet? I'm not sure if some extra-work should be done from my side, I don't see any review to validate or what so ever but both git and NodeJS/TS are my friend.

[atinux]

Updated and merged, thank you very much ❤️