Don't relinquish root until *after* we actually start listening

Fixes #118

Forgot that listen is technically async; it worked fast enough on
my system that I didn't run into issues, but was able to repro
the above issue by trying to perform the op over ssh.

lib/waker.js

@@ -229,14 +229,14 @@ Waker.prototype.requestCredentials = function(callback) {
     });
     dummy.once('ready', () => {
         this.ui.logEvent('"PS4-Waker" device should now be available...');
+
+        // once we're listening, try to drop root privileges
+        if (this.ui.options['user-id'] && process.setuid) {
+            process.setuid(this.ui.options['user-id']);
+            this.ui.logEvent('Relinquished root privileges');
+        }
     });
     dummy.listen();
-
-    // once we're done, try to drop root privileges
-    if (this.ui.options['user-id'] && process.setuid) {
-        process.setuid(this.ui.options['user-id']);
-        this.ui.logEvent('Relinquished root privileges');
-    }
 };
 
 /**