This PR adds the feature of commenting on a failed automerge. It's done by adding a conditional in `lib/workers/branch/automerge.js` which, in case of receiving `failure` or `error` from the `getBranchStatus` function, returns the "branch status error" value. Another modification is in `lib/workers/branch/index.js`, which is an adition to the failure response of the `tryBranchAutomerge` function. The added functionality is the ability to add a comment to the PR which had a failure automerging. In case of receiving the aforementioned "branch status error" value, to the comment is appended a note which emphasize the fact that there're multiple failed status checks.

Closes #1934 

Renames currentVersion to currentValue, newVersion to newValue, newVersionMajor to newMajor, and newVersionMinor to newMinor.

Closes #2032

This PR follows up and fixes #1968

The previous PR didn't behave correctly as it was expecting Github Enterprise to ALWAYS been configured and that the github.com token was available in the `GITHUB_COM_TOKEN` env variable.
But for non GHE project `GITHUB_COM_TOKEN` is not defined and github.com token is available at the `GITHUB_TOKEN` env variable instead.

This updated PR fix this issue and avoid further problems by prioritising `github.com` over GHE.
Now the code is NOOP if no `GITHUB_ENDPOINT` is configured.

If it's configured, instead, now the codes assumes that, by DEFAULT, a dependency is hosted on `github.com` so it removes `GITHUB_ENDPOINT` and use `GITHUB_COM_TOKEN` as Github token immediately.
They are restored only if needed, when a dependency is hosted on the provided GithubEnterprise.

This reverts commit f2fb2e6b.

Closes #1931

This PR splits the logic behind changelog into manager (npm) and source (github)
the manager provides the repo url + versions
the source consumes the manager info and generates changelog info

Closes #1911

Adds new option “pr-comment” for `automergeType` and a new option `automergeComment` to use in such a case.

Refactor changelog (commits) logic to separate sources, and remove the `changelog` dependency. Instead of a full copy/paste of commits, a link is now provided to the source repo.

Closes #381

Adds support for renovating docker image definitions in CircleCI 2 config files (`.circleci/config.yml`).

Closes #1714

Try to get message and body in all errors we log

fix: raise PR immediately if there are lock file errors

To ensure we list both nvm and engines when upgrading node

Adds initial support for `.nvmrc` renovation. If the existing value is a fully-specified semver version then it will be upgraded, otherwise left alone.

Closes #1270 

Enables a “banner” at the top of PRs. Must be set inside a config.js to work.

Adds support for upgrading `node` version in `package.json` > `engines` if the current version is pinned.
- Does not convert from range to pin
- Ignores ranges
- Does not upgrade major versions

Instead of deleting the GITHUB_TOKEN when we find GHE configured, replace it with GITHUB_COM_TOKEN for the purposes of retrieving release notes and commit history.

Workaround for #1500 but does not close it.