Scrollable's horizontal={false} is not working

[teru-mi]

Issue summary

Scrollable's horizontal={false} is not working. I put codesandbox down below.

Expected behavior

It shouldn't scrollable horizontally.

Actual behavior

Steps to reproduce the problem

1. First step
2. Second step

Reduced test case

https://codesandbox.io/embed/stoic-sun-54yfjm?fontsize=14&hidenavigation=1&theme=dark

Specifications

• Are you using the React components? (Y/N):
• Polaris version number:
• Browser:
• Device:
• Operating System: