What is the syntax used to bundle multiple dlls in "bin" in project.json

I have an ASP.Net 5 (vNext) solution that needs to reference many locally built DLLs. I have tried using different versions of the syntax in the project.json file to specify the DLL. My attempts have either ended up with syntax errors, or (most promising) say that "cannot distinguish Newtonsoft.Json.Linq.JArray to Newtonsoft.Json.Linq.JToken".

The syntax that generated the error above was

"frameworks":
{
    "aspnet50":
    {
        "bin":
        {
            "assembly":
            [
                "C:\\foo.dll",
                "C:\\bar.dll"
            ],
            "pdb":
            [
                "C:\\foo.pdb",
                "C:\\bar.pdb"
            ]
        }
    }
},