Update tinygltf submodule to fix a bug with exported attributes (isl-…

…org#1711)

* Update tinygltf submodule to fix a bug with exported attributes.

Due to forgotten initializers, glTF files were exported with random
values for the normalized attribute field, which caused them to not be
valid and broke various importers. The change is done conservatively,
not updating to latest, only to these two commits of interest:

syoyo/tinygltf@ae93649
syoyo/tinygltf@2e8a115

* Update tinygltf once more to fix compiler warnings.