Better browser checking and source update fix

[frnsys]

Tried using this library today, ran into a couple issues that this pull request should fix.

• the node environment check misses if it's a browser since now browsers have a process variable
• the make update-source command pulled the latest recastnavigation and tries to apply patches that are inappropriate for that revision

I'm still not able to get the library to work (abort errors when trying to build the navmesh) but these fixes might help others.

[vincent]

Thank you !