Fix background message handler return values for promos. Add license …

…and header to Plus Promo Modal sass file.

app/shared-components/PlusPromoModal/PlusPromoModal.scss

@@ -1,3 +1,17 @@
+/**
+ * Plus Promo Modal Sass
+ *
+ * Ghostery Browser Extension
+ * https://www.ghostery.com/
+ *
+ * Copyright 2019 Ghostery, Inc. All rights reserved.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0
+ */
+
+// Plus Promo Modal
 $standard-font-family: Roboto, "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
 
 .PlusPromoModal__gold-ghostie-badge {

src/background.js

@@ -1080,15 +1080,15 @@ function onMessageHandler(request, sender, callback) {
 	}
 	if (name === 'promoModals.sawPlusPromo') {
 		promoModals.recordPlusPromoSighting();
-		return true;
+		return false;
 	}
 	if (name === 'promoModals.sawInsightsPromo') {
 		promoModals.recordInsightsPromoSighting();
-		return true;
+		return false;
 	}
 	if (name === 'promoModals.turnOffPromos') {
 		promoModals.turnOffPromos();
-		return true;
+		return false;
 	}
 }