fix date conversion

Author: BRONSOLO

plotly/plotlyfig_aux/helpers/convertDate.m

@@ -1,3 +1,3 @@
 function converted = convertDate(date)
-   converted = (date - datenum(1970,0,0))*1000*60*60*(23 + 56/60);
+   converted = (date - datenum(1969,12,31,19,00,00))*1000*60*60*24;
 end