add missing Reference Include

Author: xbelt

Source/Tests/Exceptionless.Tests.csproj

@@ -100,6 +100,7 @@
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\..\packages\Microsoft.AspNet.WebApi.Client.5.2.3\lib\net45\System.Net.Http.Formatting.dll</HintPath>
     </Reference>
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Web.Http, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\..\packages\Microsoft.AspNet.WebApi.Core.5.2.3\lib\net45\System.Web.Http.dll</HintPath>