Added case-insentive support for the 'mode' argument in both directions() and distance()

This supports mode:UPPERCASE('WALKING',etc.) & mode:LOWERCASE('walking',etc.). 
Earlier, it was just supporting LOWERCASE('walking','bicycling',etc). I think this is necessary as it gives the developer a little bit of freedom and reduces confusion for starters(like me.. ) :)

Case: 
Use(argument)->Result(In the JSONresponse)
mode = 'WALKING'->"travel_mode":"DRIVING"
mode = 'walking'->"travel_mode":"WALKING"