[node] Enable npm to build mapbox-gl-native package from source

- Allow node bindings to be built if git submodules cannot be checked out
 - Made geojsonvt a mason package instead of a git submodule
 - Use globally installed mason if it cannot be checked out via git submodules

.gitmodules

@@ -14,6 +14,3 @@
 	path = platform/ios/vendor/SMCalloutView
 	url = https://github.com/nfarina/calloutview.git
 
-[submodule "src/mbgl/util/geojsonvt"]
-	path = src/mbgl/util/geojsonvt
-	url = https://github.com/mapbox/geojson-vt-cpp