Drop hangfire.core to 1.8.0 so we're not forcing people to use the version that has just been released

Author: dmitry-vychikov

src/Hangfire.PostgreSql/Hangfire.PostgreSql.csproj

@@ -35,7 +35,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Hangfire.Core" Version="1.8.4" />
+    <PackageReference Include="Hangfire.Core" Version="1.8.0" />
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
     <PackageReference Include="Npgsql" Version="6.0.0" />
   </ItemGroup>