Updated Javadoc for DeckPanel.getVisibleWidget()

Fixes issue 7680.

Change-Id: I457b2238ee2f36b0958fed47ed012329a860e0d1
Review-Link: https://gwt-review.googlesource.com/#/c/1720/

Review by: goktug@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11460 8db76d5a-ed1c-0410-87a9-c151d255dfc7
1 file changed