[react-jss]: Dynamic expanded styles are not updated correctly

__Expected behavior:__
Dynamic styles should correctly override the previously applied styles.

__Describe the bug:__
Dynamic styles did not correctly override the previously applied styles.

__Codesandbox link:__
https://codesandbox.io/s/742q2630yj ( Click "All Borders" button to toggle between two sets of styles )

__Versions (please complete the following information):__
- jss: 10.0.0-alpha.12
- Browser [e.g. chrome, safari]: chrome
- OS [e.g. Windows, macOS]: Windows
Feel free to add any additional versions which you may think are relevant to the bug.