make sure that when things go bad in run.py, publish.py finds out.

before, if exceptions happened in run.py, but those examples had
*previously* worked, publish.py would output them. This is a bad
idea, it makes it seem like things ran OK when they didn't.
Merge pull request #37 from plotly/andrew-fix-threading

make sure that when things go bad in run.py, publish.py finds out.