readline: refactor filter() callback

Use construct that always returns a boolean for `filter()` callback.

PR-URL: #17858
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: Trott

lib/readline.js

@@ -500,9 +500,7 @@ Interface.prototype._tabComplete = function(lastKeypressWasTab) {
       }
 
       // If there is a common prefix to all matches, then apply that portion.
-      var f = completions.filter(function completionFilter(e) {
-        if (e) return e;
-      });
+      var f = completions.filter((e) => e);
       var prefix = commonPrefix(f);
       if (prefix.length > completeOn.length) {
         self._insertString(prefix.slice(completeOn.length));