fix sinon error

Author: Gaurav0

packages/ember-cli-fastboot/tests/unit/services/fastboot/shoebox-test.js

@@ -9,7 +9,7 @@ module('Unit | Service | fastboot | shoebox', function(hooks) {
   setupTest(hooks);
 
   hooks.beforeEach(function() {
-    sandbox = sinon.sandbox.create();
+    sandbox = sinon.createSandbox();
   });
 
   hooks.afterEach(function() {
@@ -90,4 +90,4 @@ module('Unit | Service | fastboot | shoebox', function(hooks) {
 
     assert.strictEqual(service.get('shoebox').retrieve('foo'), 'bar');
   });
-});
+});