Update Rx.NET to use NETStandard.Library only for netstandard1.x

Rx.NET/Source/NuSpecs/System.Reactive.Interfaces.nuspec

@@ -15,7 +15,10 @@
     <language>en-US</language>
     <tags>Rx Reactive Extensions Observable LINQ Events</tags>
     <dependencies>
-      <dependency id="NETStandard.Library" version="1.6.0" />
+     <group targetFramework="netstandard1.0">       
+        <dependency id="NETStandard.Library" version="1.6.0" />
+     </group>
+     <group targetFramework="net45" />
     </dependencies>
   </metadata>
   <files>

Rx.NET/Source/System.Reactive.Interfaces/project.json

@@ -22,11 +22,7 @@
       "includeFiles": [ "../GlobalAssemblyVersion.cs" ]
     }
   },
-
-  "dependencies": {
-    "NETStandard.Library": "1.6.0"
-  },
-
+  
   "frameworks": {
     "net45": {
       "buildOptions": {
@@ -64,6 +60,9 @@
           "USE_TIMER_SELF_ROOT",
           "PLIB"
         ]
+      },
+      "dependencies": {
+        "NETStandard.Library": "1.6.0"
       }
     }
   }