gltfpack: Fix support for old Node versions
gltfpack: Fix support for old Node versions

gltfpack.js now requires TextEncoder/TextDecoder; these were available
for quite some time now, but older node.js builds don't expose these
directly. Fortunately compatible replacements are available in util.
module.

Fixes #195.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer