y-axis of time_v_channel graph in waveform_display not correct

Created by: cheryonthetop

#128 loads data and shows the graph. But the waveform_display graph has a little problem: Notice the PMT number goes from 0 to 1, when it should go from 0 to number of channels. The code to reproduce the plot is:

import straxen    
st = straxen.contexts.xenon1t_dali(build_lowlevel=True)
run_id = '170204_1710'
df = st.get_array(run_id, "event_info")
event = df[4]
st.waveform_display(run_id, time_within=event)