doc: typo (fix #958)

Author: samcarter

doc/beamerug-frames.tex

@@ -500,7 +500,7 @@ \subsubsection{The Headline and Footline}
     Inserts the current subsection into a template.
 
     \iteminsert{\insertsubsubsection}
-    Inserts the current subsection into a template.
+    Inserts the current subsubsection into a template.
 
     \iteminsert{\insertsubsectionnavigation}\marg{width}
     Inserts a vertical navigation bar containing all subsections of the current section, with the current subsection highlighted.