Sets the default value for the reserved column to 0 (instead of null)

Fixes the error "Cannot add a NOT NULL column with default value NULL"

database/migrations/2019_12_12_131400_AlterJobsDropReserved.php

@@ -35,7 +35,7 @@ class AlterJobsDropReserved extends Migration
     public function down()
     {
         Schema::table('jobs', function (Blueprint $table) {
-            $table->tinyInteger('reserved')->unsigned()->after('attempts');
+            $table->tinyInteger('reserved')->unsigned()->default(0)->after('attempts');
         });
     }
 }