message: Move preview package of iothub to preview folder
diff: @@ -26,7 +26,7 @@ These settings apply only when `--tag=package-2018-12-preview --go` is specified
  Please also specify `--go-sdk-folder=<path to the root directory of your azure-sdk-for-go clone>`.
  ``` yaml $(tag) == 'package-2018-12-preview' && $(go)
  -output-folder: $(go-sdk-folder)/services/iothub/mgmt/2018-12-01-preview/$(namespace)
  +output-folder: $(go-sdk-folder)/services/preview/iothub/mgmt/2018-12-01-preview/$(namespace)
  ```
  ### Tag: package-2018-04 and go
  