added primary key to migrations table (#15770)

src/Illuminate/Database/Migrations/DatabaseMigrationRepository.php

@@ -136,6 +136,8 @@ public function createRepository()
             // The migrations table is responsible for keeping track of which of the
             // migrations have actually run for the application. We'll create the
             // table to hold the migration file's path as well as the batch ID.
+            $table->increments('id');
+
             $table->string('migration');
 
             $table->integer('batch');