Update recommended extension version log message

Author: jackbatzner

src/WebJobs.Script/Host/ScriptHost.cs

@@ -447,7 +447,7 @@ private void PreInitialize()
                 if (string.IsNullOrEmpty(extensionVersion))
                 {
                     throw new HostInitializationException($"Invalid site extension configuration. " +
-                        $"Please update the App Setting '{EnvironmentSettingNames.FunctionsExtensionVersion}' to a valid value (e.g. ~2). " +
+                        $"Please update the App Setting '{EnvironmentSettingNames.FunctionsExtensionVersion}' to a valid value (e.g. ~4). " +
                         $"The value cannot be missing or an empty string.");
                 }
                 else if (string.Equals(extensionVersion, "latest", StringComparison.OrdinalIgnoreCase))
@@ -1013,4 +1013,4 @@ protected override void Dispose(bool disposing)
             _logger.DisposedScriptHost(ScriptOptions.InstanceId);
         }
     }
-}
+}