Update download script for PHP sources so that the Docker build fails…

… less often

Merge pull request brefphp#618 from brefphp/fix-missing-dependency

Fix missing dependency for PSR-15 handlers

Typo

Update layer versions in tests

Update layers

Update layer versions for new runtimes

Merge pull request brefphp#580 from tristanbes/patch-1

Update case-studies.md

Update layer versions

Merge pull request brefphp#551 from brefphp/improve-deploy-docs

Improve documentation for on-boarding new users

Update layer versions