update to latest msbuild for unity

Author: davidkline-ms

Assets/MixedRealityToolkit/Utilities/Editor/PackageManifest/PackageManifestUpdater.cs

@@ -18,7 +18,7 @@ internal static class PackageManifestUpdater
         private static string[] MSBuildRegistryScopes = new string[] { "com.microsoft" };
 
         private static string MSBuildPackageName = "com.microsoft.msbuildforunity";
-        private static string MSBuildPackageVersion = "0.8.3";
+        private static string MSBuildPackageVersion = "0.9.1";
 
         /// <summary>
         /// Ensures the required settings exist in the package manager to allow for