Fix typo

doc/Language/classtut.pod

@@ -76,7 +76,7 @@ Declaring a class creates a I<type object> which, by default, is installed
 into the current package (just like a variable declared with C<our> scope).
 This type object is an "empty instance" of the class.  You've already seen
 these in previous chapters. For example, types such as C<Int> and C<Str>
-refer to the type object of one of the Perl 6 built- in classes. The example
+refer to the type object of one of the Perl 6 built-in classes. The example
 above uses the class name C<Task> so that other code can refer to it later,
 such as to create class instances by calling the C<new> method.