Update GWT version to 2.8.0 official release
Update GWT version to 2.8.0 official release

marcrh/gwt-material,guibertjulien/gwt-material,GwtMaterialDesign/gwt-material,guibertjulien/gwt-material,GwtMaterialDesign/gwt-material,GwtMaterialDesign/gwt-material,guibertjulien/gwt-material,marcrh/gwt-material,marcrh/gwt-material