Adjust article for IO::Socket::INET.accept method description.

As far as source in rakudo 2018.01 the accept method returns an instance
of IO::Socket::INET class or a subclass. Therefore it could be returned
'an' instance of IO::Socket::INET or something below in the inheritance chain.

See issue #1929

doc/Type/IO/Socket/INET.pod6

@@ -92,7 +92,8 @@ Returns a lazy list of lines read from the socket.
     method accept()
 
 In listen/server mode, waits for a new incoming connection.
-Once a new connection is established, the C<IO::Socket::INET>
-instance for consuming the connection is returned.
+Once a new connection is established, an C<IO::Socket::INET>
+instance (or a subclass instance) for consuming
+the connection is returned.
 
 =end pod