Update IntegrationTestCase::_buildRequest

Hi,

I'm not sure it's the better way to do this but the parameter __$method__ is currently not use in this function.
I was trying to test my controller : #4606

I used __$this->put('/actions/changeStatus/1.json', ['status_id' => 2])__.
But the request of the controller didn't have an environment variable __REQUEST_METHOD__.
Or more precisely, it equalled to null.

    $this->request->env('REQUEST_METHOD') // null

So these lines, that i changed, resolve this problem.

Jason.