Update heart_monitor.md

Author: qgeissmann

protocols/heart_monitor.md

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 Optical Snail Heart Rate Monitor
 ==================================
 
-**Quentin Geissmann**
+<iframe src="https://widgets.figshare.com/articles/1294198/embed?show_title=1" width="568" height="426" frameborder="0"></iframe>
 
 Monitoring physiological variables is crucial in many areas of biology.
 It is particularly difficult to study the physiology of small