Remove typo from sample-handout

sample-book.tex

@@ -519,7 +519,7 @@ The specification of the \doccmddef{sidenote} command is:
 
 Both the \docopt{number} and \docopt{offset} arguments are optional.  If you
 provide a \docopt{number} argument, then that number will be used as the
-sidenote number.  It will change of the number of the current sidenote only and
+sidenote number.  It will change the number of the current sidenote only and
 will not affect the numbering sequence of subsequent sidenotes.
 
 Sometimes a sidenote may run over the top of other text or graphics in the