Optimize release builds explicitly

Terminal.Gui/Terminal.Gui.csproj

@@ -21,6 +21,7 @@
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>portable</DebugType>
+    <Optimize>True</Optimize>
     <VersionSuffix></VersionSuffix>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">