Resolve "Density switch does not change the y_axis label"

Closes #72 (closed)

nnfwtbn/plot.py

@@ -263,6 +263,9 @@ def hist(dataframe, variable, bins, stacks, selection=None,
         if isinstance(denominator, int) and stacks[denominator] == stack:
             denominator = stack
 
+    if density:
+        uhepp_obj.y_label = "Events (a.u.)"
+
     uhepp_obj.ratio_label = ratio_label
     if ratio_range:
         uhepp_obj.ratio_min = ratio_range[0]