direction validate_snapping behavior differs by Python version

[perrygeo]

Another fun Python 2/3 issue

The _validate_snapping method returns (bearings, radii) tuples.

In Python 3, we get the correct behavior

>>> from mapbox.services import directions
>>> d = directions.Directions()
>>> d._validate_snapping([(1, 1, 1), u'unlimited'], [None, None])
([(1, 1), None], [1, 'unlimited'])

In Python 2, we get an Expection

>>> from mapbox.services import directions
>>> d = directions.Directions()
>>> d._validate_snapping([(1, 1, 1), u'unlimited'], [None, None])
------------------------------------------------------------------------
InvalidParameterError                  Traceback (most recent call last)
<ipython-input-3-1dc0bc40d399> in <module>()
----> 1 d._validate_snapping([(1, 1, 1), u'unlimited'], [None, None])

/Users/mperry/env/sdk27/lib/python2.7/site-packages/mapbox/services/directions.pyc in _validate_snapping(self, snaps, features)
     93                     except ValueError:
     94                         raise errors.InvalidParameterError(
---> 95                             'waypoint snapping should contain 3 elements: '
     96                             '(bearing, angle, range)')
     97                     self._validate_radius(radius)

InvalidParameterError: waypoint snapping should contain 3 elements: (bearing, angle, range)