Update what's new.md (#16)

dist/preview release/what's new.md

@@ -158,6 +158,7 @@
 - Added support for KHR_materials_unlit to glTF serializer ([Popov72](https://github.com/Popov72))
 - Added support for glTF Skins to glTF serializer ([Drigax](https://github.com/Drigax))
 - Added support for glTF Morph Target serialization ([Drigax](https://github.com/Drigax))
+- Fixed several bugs in stlSerializer ([aWeirdo](https://github.com/aWeirdo))
 
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