Closes #2299

Closes #2291

Pushes “getPrBody” logic into platform level to allow platforms to individually do things like text replacements and body length limiting.

Closes #2267

Adds new config option `rollbackPrs` which defaults to `true` (current behaviour). Setting to false will disable creation of rollback PRs - configurable globally, per-language, per-package, etc.

Adds support for .gitlabci.yml files. Part of the logic is same as Docker Compose files, however the “services” list is new/different so requires additional logic.

Closes #1598

"docker" in config now refers to the Docker "language", which is the parent of dockerfile, docker-compose and circleci managers.

This reverts commit 4ecbbc77.

chore: update node:8.11.3-alpine docker digest to deb628

Removes custom Docker lookup code and instead integrates it with the generic lookup routine used by other package managers. Logic for digest support was added but is used by Docker-only for now.

Closes #2081, Closes #2276

Retries every minute up to 5 times if receiving 429 from gitlab.

Closes #1578

fix: update dependency luxon to v1.3.2

Adds logic to support updating the accompanying `composer.lock` file whenever `composer.json` is updated.

Closes #2098