Update heatmap.py solving a csv reading problem.

If you export data from excel in Mac OS X to csv file, python shows the error: <code>new-line character seen in unquoted field - do you need to open the file in universal-newline mode?</code>
This issue was solved changing 'ru' by 'rU' at line 793, in open function - I have no idea why!
remove comment
change open() mode from 'ru' to 'rU'
thanks to estebanz01 169208fb767987317235428571e1232640065f16
closes #16