Does not support dotnet5.4

[Eaglef90]

When you create a ASP.Net Core 1 class library the framework name is "dotnet5.4" which does not appear to be supported by 1.3.0-beta6 as the error "The dependency MailKit 1.3.0-beta6 does not support framework .NetPlatform, Version=v5.4" is thrown.

Example project.json from the RC1 Empty project template in VS 2015

{
    "version": "1.0.0",
    "description": "JobSight.Core Class Library",
    "authors": [ "Matthew Verstraete" ],
    "tags": [ "" ],
    "projectUrl": "",
    "licenseUrl": "",
    "frameworks": {
        "dotnet5.4": {
            "dependencies": {
                "Microsoft.CSharp": "4.0.1-beta-23516",
                "System.Collections": "4.0.11-beta-23516",
                "System.Linq": "4.0.1-beta-23516",
                "System.Runtime": "4.0.21-beta-23516",
                "System.Threading": "4.0.11-beta-23516"
            }
        }
    },
    "dependencies":
    {
        "JobSight.DAL": "1.0.0",
        "MailKit": "1.3.0-beta6",
        "Newtonsoft.Json": "8.0.2",
        "System.Net.Http": "4.0.1-beta-23516",
        "System.Text.RegularExpressions": "4.0.11-beta-23516"
    }
}

[jstedfast]

it's impossible to support dotnet54 in MailKit because it's missing a ton of APIs that I need.