Gazebo sonar config aways detects the ground at 1m away

[MoffKalast]

The sonar detection cones collide with the ground at roughly 1m away from the sensor due to magni's low height. I suggest either tilting the sensors upwards by a few degrees, making the cones flatter or narrower in all directions.

Furthermore the sonar max distance is set to 3.2m instead of 4m as is the spec for HC-SR04.

I'll make a pull request with the fix if this isn't intended behaviour.