Bug Fix: #7: Device serialization for 'height' field on Ubersmith 3.0.0 fails

Device 'height' field type used to be 'int' but on Ubersmith 3.0.0, this field is an 'float'
See bug #7: https://github.com/jasonkeene/python-ubersmith/issues/7

This pull request includes setting type 'float' for fields 'depth', 'height' and 'width'