use next instead of explicit beta version

Author: michaeldyrynda

src/TailwindCssPreset.php

@@ -30,7 +30,7 @@ protected static function updatePackageArray(array $packages)
             'laravel-mix' => '^4.0.14',
             'laravel-mix-purgecss' => '^4.1',
             'laravel-mix-tailwind' => '^0.1.0',
-            'tailwindcss' => '^1.0.0-beta.4',
+            'tailwindcss' => 'next',
             'vue' => '^2.5.17',
             'vue-template-compiler' => '^2.6.4',
         ], Arr::except($packages, [