ASP.. NET 5控制台应用程序dnxcore50 missing ' system.net.http&# 39;装

我在OS X上使用visual studio代码，我试图使用System.Net.Http与dnxcore50发出HTTP请求。当我运行mcs -debug Program.cs时，我得到消息:

Program.cs(2,18):错误CS0234:类型或命名空间名称"Http"在命名空间"System.Net"中不存在。你想念System.Net吗?Http程序集引用?'

这是我的project.json:

{
"version": "1.0.0-*",
"description": "Console Application",
"authors": [
    "your name"
],
"tags": [
    ""
],
"projectUrl": "",
"licenseUrl": "",
"dependencies": {
    "Newtonsoft.Json": "7.0.1",
    "System.Net.Http": "4.0.1-beta-23217",
    "Microsoft.AspNet.WebApi.Client": "5.2.3"
},
"commands": {
    "ConsoleApplication": "ConsoleApplication"
},
"frameworks": {
    "dnx451": {},
    "dnxcore50": {
        "dependencies": {
            "Microsoft.CSharp": "4.0.1-beta-23217",
            "System.Collections": "4.0.11-beta-23217",
            "System.Console": "4.0.0-beta-23217",
            "System.Linq": "4.0.1-beta-23217",
            "System.Threading": "4.0.11-beta-23217"
        }
    }
}