Visual Studio 2013 now has an update that adds SQL Server 2014 support under Tools –> Extensions and Updates –> Updates
After installing the update under Help -> About Microsoft Visual Studio I see I now have SQL Server Data Tools 12.0.40403.0
Now SQL Server 2014 is an option in my database project settings and everything works!
Original Response:
I have the same problem. It looks like the update for Visual Studio 2013 isn't out yet :(
In the next few days the Visual Studio 2013 download will appear through the Visual Studio update channel (Tools –> Extensions and Updates –> Updates).