Fix typo "backlash" (#199)

pollen/scribblings/command.scrbl

@@ -43,7 +43,7 @@ My advice: don't knock the lozenge till you try it.
 
 @subsubsection{How MB types the lozenge}
 
-I work on Mac OS. I use @link["http://www.ergonis.com/products/typinator/"]{Typinator} to assign the @literal{◊} character to the otherwise never-used Option + Shift + backlash key combo (ordinarily assigned to @literal{»}). For that matter, I assign @literal{λ} to Option + backslash (ordinarily assigned to @literal{«}).
+I work on Mac OS. I use @link["http://www.ergonis.com/products/typinator/"]{Typinator} to assign the @literal{◊} character to the otherwise never-used Option + Shift + backslash key combo (ordinarily assigned to @literal{»}). For that matter, I assign @literal{λ} to Option + backslash (ordinarily assigned to @literal{«}).
 
 @subsubsection{DrRacket toolbar button}