Correct description of absoluteURL and webSocketURL

"absoluteURL" and "webSocketURL" are not properties. They are methods which must be called with "()" at the end in order to get the string representing the URL. That's different from getting the url using the "url" property, which is already a string property.
Update ScalaJavascriptRouting.md
Merge pull request #2203 from 6qat/patch-1

Correct description of absoluteURL and webSocketURL