WICKET-5420 Make UploadProgressBar easier to extend

Fix a typo in comments
diff --git a/wicket-examples/src/main/java/org/apache/wicket/examples/upload/UploadPage.java b/wicket-examples/src/main/java/org/apache/wicket/examples/upload/UploadPage.java
index f87174a..92e03c8 100644
--- a/wicket-examples/src/main/java/org/apache/wicket/examples/upload/UploadPage.java
+++ b/wicket-examples/src/main/java/org/apache/wicket/examples/upload/UploadPage.java
@@ -103,7 +103,7 @@
 		{
 			super(name);
 
-			// set this form to multipart mode (allways needed for uploads!)
+			// set this form to multipart mode (always needed for uploads!)
 			setMultiPart(true);
 
 			// Add one file input field