repl: preserve the cursor when redisplaying the prompt on SIGCONT

Otherwise the cursor position was being reset to 0, even when there was
already part of a line, which was strange.

Part of #3295.

lib/repl.js

@@ -306,7 +306,7 @@ function REPLServer(prompt, stream, eval, useGlobal, ignoreUndefined) {
   });
 
   rli.on('SIGCONT', function() {
-    self.displayPrompt();
+    self.displayPrompt(true);
   });
 
   self.displayPrompt();