Pin dependencies

The new version of NuGet can now be configured to install the latest
version of dependencies, instead of the old default to install
the lowest version. I've updated our NuGet package spec to
set an upper limit on our dependencies to account for this new behavior.

Author: carolynvs

src/corelib/corelib.nuspec

@@ -15,9 +15,9 @@
     <tags>openstack</tags>
     <dependencies>
       <group targetFramework="4.5">
-        <dependency id="Newtonsoft.Json" version="6.0.4" />
-        <dependency id="Flurl.Http.Signed" version="0.6.2.2015062601" />
-        <dependency id="Marvin.JsonPatch.Signed" version="0.7.0" />
+        <dependency id="Newtonsoft.Json" version="[6.0.1,7.0)" />
+        <dependency id="Flurl.Http.Signed" version="[0.6.2.2015062601, 0.7)" />
+        <dependency id="Marvin.JsonPatch.Signed" version="[0.7.0]" />
       </group>
     </dependencies>
   </metadata>