FS-7966: fix mod_managed reference

src/mod/languages/mod_managed/mod_managed.2015.vcxproj

-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug_CLR|Win32">
@@ -341,11 +341,11 @@
     <ProjectReference Include="..\..\..\..\w32\Library\FreeSwitchCore.2015.vcxproj">
       <Project>{202d7a4e-760d-4d0e-afa1-d7459ced30ff}</Project>
     </ProjectReference>
-    <ProjectReference Include="managed\FreeSWITCH.Managed.2012.csproj">
+    <ProjectReference Include="managed\FreeSWITCH.Managed.2015.csproj">
       <Project>{834e2b2f-5483-4b80-8fe3-fe48ff76e5c0}</Project>
     </ProjectReference>
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
\ No newline at end of file
+</Project>