add shadow so that we can test @tailwind base

We were only using `font-bold`, but that doesn't require any base rules.
We try to only inject rules that are required, even for `base` related
rules.
Adding `shadow` will ensure that we can test that `base` rules have been
added.

Author: RobinMalfait

integrations/tailwindcss-cli/tests/cli.test.js

@@ -12,7 +12,7 @@ let EXECUTABLE = 'node ../../lib/cli.js'
 
 describe('Build command', () => {
   test('--output', async () => {
-    await writeInputFile('index.html', html`<div class="font-bold"></div>`)
+    await writeInputFile('index.html', html`<div class="font-bold shadow"></div>`)
 
     await $(`${EXECUTABLE} --output ./dist/main.css`)