need to explicitly include an empty net45 section to indicate no deps,...

need to explicitly include an empty net45 section to indicate no deps, otherwise it assumes net40 deps still apply

StackExchange.Redis.nuspec

@@ -19,6 +19,8 @@
         <dependency id="Microsoft.Bcl.Async" version="1.0.168"/>
         <dependency id="Microsoft.Bcl.Build" version="1.0.14"/>
       </group>
+      <group targetFramework="net45">
+      </group>
     </dependencies>
   </metadata>
   <files>