[gloassary] grammar fix by diakopter++

Author: moritz

lib/glossary.pod

@@ -68,7 +68,7 @@ attributes, and an instance carries it forward into the real world.
 
 =head1 Invocant
 
-The object that a method is called is called the I<invocant> in Perl 6.
+The object on which a method is called is called the I<invocant> in Perl 6.
 It is what C<self> refers to in a method.
 
     say 'str'.uc;   # 'str' is the invocant of method uc