Timeout option breaks rebuild decision

[mberz]

Scons does not properly detect whether a notebook needs to be rebuilt when using the timeout option:
scons timout=360
Instead all notebooks will be rebuilt regardless if changes were made or not.
Directly providing a dict {'timeout':'360'} to the setup in the SConstruct file does result in the same issue.
Issue occured on Arch Linux using Miniconda with Python 3.7.