chore: bump serve-static and express in /examples/mern-cdk-ci-cd/mern/client (#355)

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

Author: dependabot[bot]