Back packages.config off to Dev14-compatible version.

Author: brettfo

packages.config

@@ -30,7 +30,7 @@
   <package id="VisualCppTools" version="14.0.24519-Pre"/>
   <package id="Newtonsoft.Json" version="6.0.8"/>
   <package id="Microsoft.FSharp.TupleSample" version="1.0.0-alpha-161121"/>
-  <package id="Microsoft.VSSDK.BuildTools" version="15.0.25929-RC2" />
+  <package id="Microsoft.VSSDK.BuildTools" version="15.0.25907-RC2" />
 
   <!-- Annoyingly the build of FSharp.Compiler.Server.Shared references a Visual Studio-specific attribute -->
   <!-- That DLL is logically part of the F# Compiler and F# Interactive but is shipped as part of the Visual F# IDE Tools -->