[FIX] Fix return value documentation of Element.clone
[FIX] Fix return value documentation of Element.clone

Closes https://github.com/SAP/openui5/pull/1209
Change-Id: Ia72290b617a5b6513e3138a7d0965632a88ce716

cschuff/openui5,SAP/openui5,nzamani/openui5,SAP/openui5,SAP/openui5,cschuff/openui5,nzamani/openui5,nzamani/openui5,cschuff/openui5,SAP/openui5