Fix ToString of Task<string>

Author: Redth

source/buildtasks/support-annotations/VerifyVersionsTask.cs

@@ -83,7 +83,7 @@ public override bool Execute()
 				sb.AppendLine("The following Xamarin.Android.Support.* packages and versions were detected:");
 				sb.AppendLine();
 
-				var recommendedSupportVersion = NugetPackages.GetRecommendedSupportPackageVersion(apiLevel);
+				var recommendedSupportVersion = NugetPackages.GetRecommendedSupportPackageVersion(apiLevel).Result;
 
 				foreach (var pkg in packageVersions)
 					sb.AppendLine($"    {pkg.Key} ({pkg.Value})");