MAGETWO-67106: Unstable Automated test Magento\Paypal\Test\TestCase\InContextExpressCheckoutFromShoppingCartTest failed on variation InContextExpressCheckoutFromShoppingCartTestVariation1

 - Fixed failed static js test

Author: YevSent

app/code/Magento/Paypal/view/frontend/web/js/in-context/button.js

@@ -12,6 +12,8 @@ define(
         Component,
         $
     ) {
+        'use strict';
+
         return Component.extend({
 
             defaults: {},