Fix typo in writing_tools.py

[p4xel]

rmc crashing when converting to SVG. Traceback shows error "AttributeError: type object 'Pen' has no attribute 'ERASE_AREA'"

[Azeirah]

@ricklupton This can be merged immediately. It's the most common issue in all of rmc whaha

[ricklupton]

Thanks @p4xel and @Azeirah, I can merge this, but it would be good to add a test file that demonstrates the problem -- I think the ones currently in tests/rm maybe don't ever use the eraser, so this wasn't caught by the tests? If you have a very simple rm file that causes the issue (e.g. just draw a line and then use the eraser to remove part) and can add that to the test files, that would be useful too.

[p4xel]

@ricklupton I don't have the device to try, it is broken. I directly dumped contents of the eMMC chip and tried converting recovered files. I can email you the problematic file if you need it.

[Azeirah]

@ricklupton I don't have the device to try, it is broken. I directly dumped contents of the eMMC chip and tried converting recovered files. I can email you the problematic file if you need it.

No need. I already made the file and added a PR

#24