message: docs(dom-test-kit): fix readme code example
diff: ```ts
  /* test.ts */
  import { StylableDOMUtil } from '@stylable/dom-test-kit';
  -import style from './my-component.st.css';
  +import * as stylesheet from './my-component.st.css';
  -const domUtil = new StylableDOMUtil(style, document.body);
  +const domUtil = new StylableDOMUtil(stylesheet, document.body);
  const partElement = domUtil.select('.part');
  +if (partElement) {
  domUtil.hasStyleState(partElement, 'loading');
  +}
  ```
  ## What does it do?
  