Update dependency StackExchange.Redis to v2.8.0

Author: renovate[bot]

StackExchangeRedis/NHibernate.Caches.StackExchangeRedis/NHibernate.Caches.StackExchangeRedis.csproj

@@ -24,7 +24,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="all" />
     <PackageReference Include="NHibernate" Version="5.2.0" />
-    <PackageReference Include="StackExchange.Redis" Version="2.0.495" />
+    <PackageReference Include="StackExchange.Redis" Version="2.8.0" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="../../readme.md">