Circle-CI: Missing characters in tracebacks

[mgeier]

For whatever reason, the first line of dashes and the space between the exception class and the word Traceback in the second line is missing.

An example can be seen in https://32-46379698-gh.circle-artifacts.com/0/nbsphinx.pdf#subsection.7.3:

It is supposed to look like this (which was generated on RTD from the same commit):

This happens in both HTML and PDF output.