Fix jQuery import in Nuxeo UI elements test

16:37:51 chrome 57                ✓ test/nuxeo-notifications-toggle-button.html » <nuxeo-notifications-toggle-button> » when a document is not subscribed » toggle should subscribe the document
16:37:51 chrome 57                ✖ Test Suite Initialization
16:37:51 
16:37:51   jQuery is not defined
16:37:51     <unknown> at   <unknown> at /components/select2/select2.js:39:0
16:37:51 
16:37:51 chrome 57                Tests failed: Error thrown outside of test function: jQuery(...).val(...).select2 is not a function
16:37:51       HTMLElement._initSelect2 at /components/nuxeo-ui-elements-master/widgets/nuxeo-select2-behavior.html:292
16:37:51           HTMLElement.attached at /components/nuxeo-ui-elements-master/widgets/nuxeo-select2.html:86
16:37:51                      <unknown> at /components/polymer/polymer-micro.html:279
16:37:51               Object.whenReady at /components/polymer/polymer-micro.html:110
16:37:51   HTMLElement.attachedCallback at /components/polymer/polymer-micro.html:270
16:37:51   HTMLElement.attachedCallback at /components/polymer/polymer-mini.html:181
16:37:51         HTMLElement.createFrom at /components/test-fixture/test-fixture.html:208
16:37:51        HTMLElement.<anonymous> at /components/test-fixture/test-fixture.html:176
16:37:51        HTMLElement.forElements at /components/test-fixture/test-fixture.html:270
16:37:51 Test run ended in failure: Error thrown outside of test function: jQuery(...).val(...).select2 is not a function
16:37:51       HTMLElement._initSelect2 at /components/nuxeo-ui-elements-master/widgets/nuxeo-select2-behavior.html:292
16:37:51           HTMLElement.attached at /components/nuxeo-ui-elements-master/widgets/nuxeo-select2.html:86
16:37:51                      <unknown> at /components/polymer/polymer-micro.html:279
16:37:51               Object.whenReady at /components/polymer/polymer-micro.html:110
16:37:51   HTMLElement.attachedCallback at /components/polymer/polymer-micro.html:270
16:37:51   HTMLElement.attachedCallback at /components/polymer/polymer-mini.html:181
16:37:51         HTMLElement.createFrom at /components/test-fixture/test-fixture.html:208
16:37:51        HTMLElement.<anonymous> at /components/test-fixture/test-fixture.html:176
16:37:51        HTMLElement.forElements at /components/test-fixture/test-fixture.html:270