message: Fix version in meshoptimizer.h header comment
diff: /**
  - * meshoptimizer - version 0.11
  + * meshoptimizer - version 0.12
  *
  * Copyright (C) 2016-2019, by Arseny Kapoulkine (arseny.kapoulkine@gmail.com)
  * Report bugs and download new versions at https://github.com/zeux/meshoptimizer
  