Do not close readline after reading remote debugging port

Closing readline interface results in closing underlying
stream. We don't want this.

lib/Browser.js

@@ -155,9 +155,8 @@ function waitForRemoteDebuggingPort(chromeProcess) {
     const match = line.match(/^DevTools listening on .*:([\d]+)$/);
     if (!match)
       return;
-    fulfill(Number.parseInt(match[1], 10));
     rl.removeListener('line', onLine);
-    rl.close();
+    fulfill(Number.parseInt(match[1], 10));
   }
 }