Sphinx needs to be upgraded to at least 1.4.2

Ther e is a bug fixed on that patch release: https://github.com/sphinx-doc/sphinx/commit/62723872bce3527e2a0d5a04bf255fcf076f1950

Without the fix, if you don't have dvipng installed, a cryptic error message is printed since the warning is ill-formatted:

  File "/scratch/aanjos/conda/envs/dev35/lib/python3.5/site-packages/Sphinx-1.4.1-py3.5.egg/sphinx/ext/imgmath.py", line 181, in render_math
    image_translator, image_translator_executable,
TypeError: not enough arguments for format string

@amohammadi: is it possible?