fix bin edge

Author: jingjie-li

ecephys_spike_sorting/modules/quality_metrics/metrics.py

@@ -675,7 +675,7 @@ def presence_ratio(spike_train, min_time, max_time, num_bins=100):
 
     h, b = np.histogram(spike_train, np.linspace(min_time, max_time, num_bins))
 
-    return np.sum(h > 0) / num_bins
+    return np.sum(h > 0) / (num_bins - 1)
 
 
 def firing_rate(spike_train, min_time = None, max_time = None):