Not all UTF-8 special chars are supported

We use node-canvas and it seems that they don't have a font fallback handling implemented, yet:
- https://github.com/LearnBoost/node-canvas/issues/38
- https://github.com/LearnBoost/node-canvas/issues/193
- https://github.com/LearnBoost/node-canvas/issues/266
