Add @since to isWindowsPhone(). (#14425)

Change-Id: Ia4c212ead39d7b71c56db586c0a8559935cae263

server/src/com/vaadin/server/WebBrowser.java

      * @return true if the user is using Windows Phone, false if the user is not
      *         using Windows Phone or if no information on the browser is
      *         present
+     * @since 7.3.2
      */
     public boolean isWindowsPhone() {
         return browserDetails.isWindowsPhone();

shared/src/com/vaadin/shared/VBrowserDetails.java

      * Tests if the browser is run on Windows Phone.
      * 
      * @return true if run on Windows Phone, false otherwise
+     * @since 7.3.2
      */
     public boolean isWindowsPhone() {
         return isWindowsPhone;