mapboxgl global check will crash

[tmcw]

mapbox-gl-directions/src/directions.js

Line 1 in 5001f62

if (!mapboxgl) throw new Error('include mapboxgl before mapbox-gl-directions.js');

if (!mapboxgl) throw new Error('include mapboxgl before mapbox-gl-directions.js');

If mapboxgl is not defined, this will throw a referenceerror, not the error it looks like it'll throw. A correct check would be

if (typeof mapboxgl === 'undefined') throw new Error('include mapboxgl before mapbox-gl-directions.js');

!mapboxgl is a value check, not an existence check: referencing a non-bound name will always throw.

[tmcw]

Fixed in #86