upgrading nhib ref to 5.5.x

Author: RogerKratz

Src/NHibernate.Envers/NHibernate.Envers.csproj

@@ -18,6 +18,6 @@
     <DebugType>Portable</DebugType>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="NHibernate" Version="[5.4.0, 5.5.0)" />
+    <PackageReference Include="NHibernate" Version="[5.5.0, 5.6.0)" />
   </ItemGroup>
 </Project>