fix: _malloc errors when building with emscripten 2.0.4

[ianpurvis]

Fixes compound shape test errors

[ianpurvis]

@kripken Hi... I accidentally caught this issue while testing a PR in my fork. Since CI always rolls with latest emscripten, I am thinking about how to better catch configuration breakage like this. A nightly heartbeat build with ubuntu?

> AMMO_PATH=builds/ammo.js ava


  compoundShape › compound shape

  tests/compoundShape.js:69

   68:   // Create convex hull shape                        
   69:   var convexHullShape = new Ammo.btConvexHullShape();
   70:   vec.setValue(1, 1, 1);                             

  Error thrown in test:

  TypeError {
    message: 'b._malloc is not a function',
  }

  › cB (builds/ammo.js:514:417)
  › new cC (builds/ammo.js:656:342)
  › tests/compoundShape.js:69:25

  ─

  1 test failed

[kripken]

If it's easy to set up more testing that might help. But not sure it's worth it - this will be pretty rare, and not the end of the world if we notice it the next time we happen to run CI, I think.

[ianpurvis]

That's a good point... let's leave as is unless we reach enough issue to escalate it. 👍