Multiple inititalize in Lumen module

Hey Guys!

I'm here again with an another issue with the Lumen module. When I'd like to make tests that contains more than one facade mocks, then the second mock won't be applied (it remains the original class).

for example:
```php
// this is a facade mock:
\AnyNamespace\Facades\Classname::shouldReceive('command1')->andReturnTrue();
$I->sendGET('/path');

// this isn't:
\AnyNamespace\Facades\Classname::shouldReceive('command2')->andReturnTrue();
$I->sendGET('/path');
```
...because the Lumen connector initialize the client again after the second REST call (see doRequest method below), and this function will clear the previously resolved instances.

```php
// in Codeception/Lib/Connector/Lumen.php
public function __construct($module)
{
...
// constructor already initialize the module
$this->initialize();
}
...
protected function doRequest($request)
{
// firstRequest is true by default
if (!$this->firstRequest) {
// I really don't know why suppose to re-initialize the whole module,
// it's already initilaized in the constructor method
$this->initialize($request);
}
$this->firstRequest = false;
....
}

private function initialize($request = null)
{
....
if (class_exists(Facade::class)) {
// this will drop all previously resolved facades,
// and won't let my tests run correctly
Facade::clearResolvedInstances();
}
....
```
The whole firstRequest check should be removed in my opinion. I can make a PR for this.

* Codeception version: 2.5.6
* PHP Version: 7.2.13