Bump src/external/tinyxml2 from 312a809 to a0f66fd (#68)

Bumps [src/external/tinyxml2](https://github.com/leethomason/tinyxml2) from `312a809` to `a0f66fd`.
- [Release notes](https://github.com/leethomason/tinyxml2/releases)
- [Commits](leethomason/tinyxml2@312a809...a0f66fd)

---
updated-dependencies:
- dependency-name: src/external/tinyxml2
  dependency-type: direct:production
...

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