Error when someone tries to use

Author: adamwathan

src/lib/substituteTailwindAtRules.js

@@ -13,6 +13,11 @@ export default function(
 ) {
   return function(css) {
     css.walkAtRules('tailwind', atRule => {
+      if (atRule.params === 'preflight') {
+        // prettier-ignore
+        throw atRule.error("`@tailwind preflight` is not a valid at-rule in Tailwind v1.0, use `@tailwind base` instead.", { word: 'preflight' })
+      }
+
       if (atRule.params === 'base') {
         atRule.before(updateSource(pluginBase, atRule.source))
         atRule.remove()