Close documentation comment accidentally left open

Fix an accidental removal of the closing comment marker in
a3673be155.

See https://github.com/wxWidgets/wxWidgets/pull/730

interface/wx/zipstrm.h

@@ -619,7 +619,7 @@ public:
         wxZIP_FORMAT_DEFAULT even if a ZIP64 will end up being created).
 
         @since 3.1.1
-
+    */
     wxZipArchiveFormat GetFormat() const;
 };