Fix ZSH syntax error when loading .env

The `source .env` will throw the following warning with the previous
code:

```
.env:21: command not found: cla,join_ccla,tools,fieri,announcemen
```

It will also fail to set **$FEATURES** correctly.
Merge pull request #805 from tubbo/fix-dotenv-warning-on-zsh

Fix ZSH syntax error when loading .env