Build 3.0 branch on Travis as well.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76541 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't build drawing test plugin in static builds.

Static wxWidgets library can't be used in dynamically loaded plugin, simply
don't build it in this case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76542 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775