Use valid syntax in examples, avoid "..."

Author: jpsacha

ReadMe.md

@@ -288,12 +288,9 @@ new BusyWorker("Simple Task", parentWindow).doTask { () =>
 Here is a little more elaborated example. It updates a progress message and progress indicator.
 
 ```scala
-val buttonPane: Pane =
-...
-val progressLabel: Label =
-...
-val progressBar: ProgressBar =
-...
+val buttonPane: Pane = ???
+val progressLabel: Label = ???
+val progressBar: ProgressBar = ???
 
 val busyWorker = new BusyWorker("BusyWorker Demo", buttonPane) {
   progressLabel.text <== progressMessage