Fix yarn build command
Fix yarn build command

This fixes the following error:

```
vagrant@true:/var/www/true/current/client$ yarn build
yarn run v1.5.1
warning package.json: No license field
$ react-scripts build
Creating an optimized production build...
Failed to compile.

Module not found: Error: Can't resolve './index.css' in '/var/www/true/current/client/src'
```

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