Added MacOS v10.13 to the list of known versions

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/735102

Author: jstedfast

Xamarin.MacDev/MacOSXSdk.cs

@@ -33,12 +33,13 @@ namespace Xamarin.MacDev
 	public class MacOSXSdk
 	{
 		List<MacOSXSdkVersion> knownOSVersions = new List<MacOSXSdkVersion> {
-			new MacOSXSdkVersion (new [] { 10, 7 }),
-			new MacOSXSdkVersion (new [] { 10, 8 }),
-			new MacOSXSdkVersion (new [] { 10, 9 }),
-			new MacOSXSdkVersion (new [] { 10, 10 }),
-			new MacOSXSdkVersion (new [] { 10, 11 }),
-			new MacOSXSdkVersion (new [] { 10, 12 }),
+			MacOSXSdkVersion.V10_7,
+			MacOSXSdkVersion.V10_8,
+			MacOSXSdkVersion.V10_9,
+			MacOSXSdkVersion.V10_10,
+			MacOSXSdkVersion.V10_11,
+			MacOSXSdkVersion.V10_12,
+			MacOSXSdkVersion.V10_13
 		};
 
 		static readonly Dictionary<string, DTSdkSettings> sdkSettingsCache = new Dictionary<string, DTSdkSettings> ();

Xamarin.MacDev/MacOSXSdkVersion.cs

@@ -197,7 +197,7 @@ public MacOSXSdkVersion ResolveIfDefault (MacOSXSdk sdk)
 		public static readonly MacOSXSdkVersion V10_10 = new MacOSXSdkVersion (10, 10);
 		public static readonly MacOSXSdkVersion V10_11 = new MacOSXSdkVersion (10, 11);
 		public static readonly MacOSXSdkVersion V10_12 = new MacOSXSdkVersion (10, 12);
-		public static readonly MacOSXSdkVersion V10_13 = new MacOSXSdkVersion(10, 13);
+		public static readonly MacOSXSdkVersion V10_13 = new MacOSXSdkVersion (10, 13);
 
 		public static readonly MacOSXSdkVersion Cheetah = V10_0;
 		public static readonly MacOSXSdkVersion Puma = V10_1;