Fix TypeError in TokenMissing class (call to parent)

When the TokenMissing exception is raised, a TypeError exception is raised: `TypeError: super(type, obj): obj must be an instance or subtype of type`.

This is because when calling the parent ValueError class, TokenRequestDenied is passed to super() instead of TokenMissing. This is probably due to a bad copy&paste from the code of the TokenRequestDenied right above.