[5.4] fix using --database option in the migrate command

[themsaid]

This line already existed in 5.3, we need it to instruct the resolver to use the given connection when running the migration, the resolveConnection() method is used only when the grammar supports schema transactions:

protected function runMigration($migration, $method)
{
    $connection = $this->resolveConnection(
        $migration->getConnection()
    );

    $callback = function () use ($migration, $method) {
        $migration->{$method}();
    };

    $this->getSchemaGrammar($connection)->supportsSchemaTransactions()
                ? $connection->transaction($callback)
                : $callback();
}

In case it doesn't, we need to instruct the connection resolver to use the given connection.

[taylorotwell]

Merging for now but can you explain a bit more. To me when I was reviewing the code it felt really strange to set the default connection for the remainder of the process.