Updates clientScript instructions to use module (testing-library#411)

* Updates clientScript instructions to use module module is preferable to abs file path as it works with workspaces etc. * Fixes missing brackets around module

Author: theinterned

docs/testcafe-testing-library/intro.md

@@ -27,7 +27,7 @@ Add the following to your .testcaferc.json file:
 
 ```json
  "clientScripts": [
- "./node_modules/@testing-library/dom/dist/@testing-library/dom.umd.js"
+ { "module": "@testing-library/dom/dist/@testing-library/dom.umd.js" }
  ],
 ```