Changing the weather to a thunderstorm outputs "Changing to rain and thunder" instead of "Changing to thunderstorm"

Steps to reproduce:

1. Play any world with cheats enabled
2. Press chat button, then click the slashes button
3. Click the "Thunderstorm" button and enter

Observed results:
The command outputs "Changing to rain and thunder" instead of "Changing to thunderstorm".

Expected results:
The command outputs "Changing to thunderstorm".