Basically it's due to the html_use_smartypants
option which is turned on by default (see doc). In your case you would want to turn it off.
In conf.py
, find the line
#html_use_smartypants = True
And change it to
html_use_smartypants = False
EDIT:
html_use_smartypants
has been deprecated and smartquotes
should be used instead.