ConfigServer: Update the configuration cache on file changes

We were only notifying clients about the change, but didn't actually
update the internal cache in ConfigServer itself.

Thanks to "The Grey One" for pointing this out. :^)

Userland/Services/ConfigServer/ClientConnection.cpp

@@ -50,6 +50,8 @@ static Core::ConfigFile& ensure_domain_config(String const& domain)
                 }
             }
         }
+        // FIXME: Refactor this whole thing so that we don't need a cache lookup here.
+        s_cache.get(domain).value()->config = new_config;
     };
     auto cache_entry = make<CachedDomain>(domain, config, watcher_or_error.release_value());
     s_cache.set(domain, move(cache_entry));