Fixed Py3 incompatibility in core/util.py
Fixed Py3 incompatibility in core/util.py

ioam/holoviews,basnijholt/holoviews,mjabri/holoviews,vascotenner/holoviews,basnijholt/holoviews,ioam/holoviews,mjabri/holoviews,vascotenner/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews,mjabri/holoviews