Fix build on .Net Core 2.x

Emby.Drawing/Emby.Drawing.csproj

@@ -17,4 +17,9 @@
     <Compile Include="..\SharedVersion.cs" />
   </ItemGroup>
 
+  <PropertyGroup>
+      <!-- We need at least C# 7.1 for the "default literal" feature-->
+    <LangVersion>latest</LangVersion>
+  </PropertyGroup>
+
 </Project>