Travis CI: site documentation update at 2014-09-12 10:43:45 UTC.

Commit: https://github.com/urho3d/Urho3D/commit/36175d471f239970829a7def3e3d8d75fcacd8e4

Message: Make attribute accessor base class abstract to avoid unused parameter warnings when including Attribute.h. The base class is not useful in any case.