godot: HTML5 project export no longer runs in 3.0 beta2.

Godot version: 3.0 beta2

OS/device including version: Exported on Windows 10 Pro v1709. Attempted to run on latest versions of Google Chrome and Mozilla Firefox.

Issue description: HTML5 exported project (with updated beta2 export templates) fails to run in browser with 2 errors.

**ERROR**: exit(0) implicitly called by end of main(), but noExitRuntime, so not exiting the runtime (you can use emscripten_force_exit, if you want to force a true shutdown)
'ccall' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)

Saw this environment variable in platform/javascript/detect.py however I suspect I do not have the requisite knowledge to re-compile the app and templates properly, or understand what other dependencies this might have.

Steps to reproduce: Load a project and export project to HTML5 with default settings.

Minimal reproduction project: Pong in the Godot demo projects, for example.

• I searched the existing GitHub issues for potential duplicates.