correction for catch_warnings on python 3
correction for catch_warnings on python 3

acq4/acq4,acq4/acq4,ericdill/pyqtgraph,acq4/acq4,campagnola/acq4,campagnola/acq4,mgraupe/acq4,pmaunz/pyqtgraph,meganbkratz/acq4,nmearl/pyqtgraph,ericdill/pyqtgraph,mgraupe/acq4,mpvismer/pyqtgraph,meganbkratz/acq4,mpvismer/pyqtgraph,mgraupe/acq4,campagnola/acq4,mgraupe/acq4,mgraupe/acq4,campagnola/acq4,meganbkratz/acq4,pmaunz/pyqtgraph,pbmanis/acq4,pbmanis/acq4,pbmanis/acq4,meganbkratz/acq4,ericdill/pyqtgraph,pbmanis/acq4,nmearl/pyqtgraph,acq4/acq4