Fix Numpy FutureWarning.
Fix Numpy FutureWarning.

Don't accidentally compare an array to string. Fixes issue #243.
mpvismer/pyqtgraph,mpvismer/pyqtgraph,ericdill/pyqtgraph,nmearl/pyqtgraph,meganbkratz/acq4,ericdill/pyqtgraph,pbmanis/acq4,mgraupe/acq4,pmaunz/pyqtgraph,campagnola/acq4,mgraupe/acq4,mgraupe/acq4,acq4/acq4,pbmanis/acq4,meganbkratz/acq4,acq4/acq4,pmaunz/pyqtgraph,acq4/acq4,meganbkratz/acq4,meganbkratz/acq4,campagnola/acq4,ericdill/pyqtgraph,mgraupe/acq4,pbmanis/acq4,campagnola/acq4,mgraupe/acq4,pbmanis/acq4,acq4/acq4,campagnola/acq4,nmearl/pyqtgraph