version bump 0.12.12: ecosystem deprecations

- node 10 `Buffer` deprecation workaround (with dependency update)
- Angular 6 global deprecation workaround (fixes #1088 h/t @cristhiank)
- BIFF8 write standard and custom properties
- TH elements in HTML string (fixes #1090 h/t @GigiSan)
- planmaker export quirks