Unix build fix dotnet#2

Author: JeffCyr

src/System.Net.NameResolution/src/System/Net/NameResolutionPal.Unix.cs

@@ -196,7 +196,7 @@ public static unsafe SocketError TryGetAddrInfo(string name, out IPHostEntry hos
             return SocketError.Success;
         }
 
-        internal static void GetAddrInfoAsync(string name, Dns.ResolveAsyncResult asyncResult)
+        internal static void GetAddrInfoAsync(string name, DnsResolveAsyncResult asyncResult)
         {
             throw new NotSupportedException();
         }