Fix custom columns, add tests (#122)

* Fix custom columns & add test

* Apply fixes from StyleCI

tests/Etc/2019_08_08_000001_add_custom_column.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class AddCustomColumn extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('tenants', function (Blueprint $table) {
+            $table->string('foo')->nullable();
+        });
+    }
+
+    public function down()
+    {
+    }
+}