Fixed html table markup.
Fixed html table markup.

The closing table markup was missing a slash. This didn't effect the
display of the notebook, but caused problems when saved to html.

InsightSoftwareConsortium/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks