[cli] stripUnit(...).replace is not a function

I'm running `npx jss-cli convert myfile.css -e es6` and I get this error:
```
stripUnit(...).replace is not a function
```

Is anyone else having this issue?

I'm doing some further investigation now.

Reproduce the reported `npx jss-cli convert myfile.css -e es6` command and trace where the `stripUnit(...).replace` error occurs. Confirm the expected ES6 conversion behavior and verify that the command completes without this error.

Written by the indexing model from the issue text.