Issue with delimiter.

[neu5]

• version: 0.10.0
• node version: 8.10.0
• yarn version: 1.7.0

Do you want to request a feature or report a bug?:
Bug
What is the current behavior?:
I tried using --delimiter flag but it doesn't work.
What is the expected behavior?:
It should work.

Example not working scripts:
NODE_ENV=development extract-messages -l=en --flat --delimiter / -o src/translations 'src/**/!(*.test).js'
NODE_ENV=development extract-messages -l=en --flat --delimiter '/' -o src/translations 'src/**/!(*.test).js'

The output json is the same, eg.

"containers.A.welcome": "Welcome!"

instead of

"containers/A/welcome": "Welcome!"