refactor: categories migration with the unique constraint

Author: ahmadhuss

database/migrations/2021_05_25_081857_create_categories_table.php

@@ -15,7 +15,7 @@ public function up()
     {
         Schema::create('categories', function (Blueprint $table) {
             $table->id();
-            $table->string('name');
+            $table->string('name')->unique();
             $table->timestamps();
         });
     }