Update documentation of toBBOX, should be decimal places not Significant Figures.

This is a slight change to the documentation of Bounds.toBBOX to reflect the actual implementation of the method.

The documentation states that results are returned to a given number of significant figures, therefore given an input 123456.789123 for 3 significant figures, this should return 123000. However the method will return 1233456.789. So, the correct description of the method should therefore be that the return values are given to a specified number of decimal places (6dp being the default).