better grammar

Author: tbrowder

doc/Language/exceptions.pod6

@@ -66,7 +66,7 @@ Please note that the match target is a role. To allow user defined exceptions
 to match in the same manner, they must implement the given role. Just existing
 in the same namespace will look alike but won't match in a C<CATCH> block.
 
-=head2  Exceptions handlers and enclosing blocks.
+=head2  Exception handlers and enclosing blocks.
 
 After a CATCH has handled the exception, the block enclosing the CATCH is left.