--label_file option for TypeTray defaults to labels.txt

[jasondunsmore]

Describe the bug

When I run:

./scripts/boxes TypeTray --sx=100 --sy=100 --h=100 --format=svg --output=/tmp/foo.svg

I get the error:

boxes: error: argument --label_file: can't open 'labels.txt': [Errno 2] No such file or directory: 'labels.txt'

Expected behavior

I didn't have to pass the --label_file option before. If I

git checkout 55616e223207d3e74564ba4e8c9898552c1611d1^

I can run:

./scripts/boxes TypeTray --sx=100 --sy=100 --h=100 --format=svg --output=/tmp/foo.svg

without error.

It seems the problem is in commit 55616e223207d3e74564ba4e8c9898552c1611d1.