Use @eof variable for ReidlineInputMethod#eof?

"IRB::InputMethod#eof?" requires eof status each user input but
"ReidlineInputMethod#eof?" used "Reline.eof?" what is singleton data.
"ReidlineInputMethod#eof?" is changed to use the result of user input.

lib/irb/input-method.rb

@@ -269,7 +269,7 @@ module IRB
     #
     # See IO#eof? for more information.
     def eof?
-      super
+      @eof
     end
 
     # Whether this input method is still readable when there is no more data to