Add missing System.Runtime.InteropServices dependency.

src/Microsoft.Net.Http.Server/project.json

@@ -20,6 +20,7 @@
         "System.IO": "4.0.11-*",
         "System.IO.FileSystem": "4.0.1-*",
         "System.Net.Primitives": "4.0.11-*",
+        "System.Runtime.InteropServices": "4.0.21-*",
         "System.Security.Claims": "4.0.1-*",
         "System.Security.Cryptography.X509Certificates": "4.0.0-*",
         "System.Security.Principal.Windows": "4.0.0-*",