Added the XML references to the mac sample

samples/MacSample/MacSample/MacSample.csproj

@@ -65,6 +65,8 @@
     <Reference Include="SkiaSharp.HarfBuzz">
       <HintPath>..\packages\SkiaSharp.HarfBuzz.1.59.0-beta\lib\portable-net45+win8+wpa81+wp8\SkiaSharp.HarfBuzz.dll</HintPath>
     </Reference>
+    <Reference Include="System.Xml" />
+    <Reference Include="System.Xml.Linq" />
   </ItemGroup>
   <ItemGroup>
     <ImageAsset Include="Assets.xcassets\AppIcon.appiconset\Contents.json" />