Failed to build pdf on Mac

[Sean Zhai]

After following all the steps successfully to build pdf for printing, the final step failed. Error messages are as below:
% make clean pdf
rm -rf /tmp.md
rm -rf /tmp.png
rm -rf book.
python src/parseBook.py -f pdf
glslViewer ./02/hello_world.frag -s 0.5 --headless -o ./02/tmp-hello_world.png
Error watching for file 0.5
Error watching for file ./02/tmp-hello_world.png
// >