fix typo

Author: skids

doc/Language/variables.pod6

@@ -929,7 +929,7 @@ variables :_>.
     my Int $i;
     # OUTPUT«===SORRY!=== Error while compiling <tmp>␤Variable definition of type Int:D (implicit :D by pragma) requires an initializer ...
     my Int $i = 1; # that works
-    { use variables :_; my Int $i; } # switch it of in this block
+    { use variables :_; my Int $i; } # switch it off in this block
 
 Please note that assigning L<Nil|/type/Nil> will revert the variable to it's
 default value. The default value of a defined constraint type is the type