build(deps-dev): bump scratch-vm

Bumps [scratch-vm](https://github.com/LLK/scratch-vm) from 0.2.0-prerelease.20200616200729 to 0.2.0-prerelease.20200618162938.
- [Release notes](https://github.com/LLK/scratch-vm/releases)
- [Commits](https://github.com/LLK/scratch-vm/commits

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>