Bump simple-git and @onflow/flow-js-testing in /lib/js/test (#129)

Removes [simple-git](https://github.com/steveukx/git-js/tree/HEAD/simple-git). It's no longer used after updating ancestor dependency [@onflow/flow-js-testing](https://github.com/onflow/flow-js-testing). These dependencies need to be updated together.


Removes `simple-git`

Updates `@onflow/flow-js-testing` from 0.3.0-alpha.13 to 0.4.0
- [Release notes](https://github.com/onflow/flow-js-testing/releases)
- [Changelog](https://github.com/onflow/flow-js-testing/blob/master/CHANGELOG.md)
- [Commits](onflow/flow-js-testing@v0.3.0-alpha.13...v0.4.0)

---
updated-dependencies:
- dependency-name: simple-git
  dependency-type: indirect
- dependency-name: "@onflow/flow-js-testing"
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Joshua Hannan <[email protected]>