A couple of tests for Random when range is used as a parameter

It will be impossible to duplicate the behavior of MRI with regard to Random#rand when a range is included as a parameter. At this point, opal doesn't distinguish between  (1..2) and (1.0..2) , so both will result in an integer returned from the range [1..2]

This means that #rand cannot return a float in the second case, which it does in MRI

Also created a test for the case #rand( 2..1) where MRI returns nil.  
The idea of running it 100 times is that random numbers are being generated. If the rng produces values outside of the specified range, the behavior is more likely to be exposed by calling the method repeatedly. Same technique is used throughout the Random spec.