docs: endorse travis cli helper

closes #99

docs/guides-ci-setup.md

@@ -2,125 +2,18 @@
 
 Enforce commit conventions with confidence by linting on your CI servers with `commitlint`.
 
- We'll use TravisCI for this guide but the principles are valid for any CI server.
-
-## Install
+?> This guide assumes you have a already configured `commitlint` for local usage. Follow the [Getting Started](readme.md#getting-started) for basic installation and configuration instructions.
 
 ```bash
-# Create a git repository if needed
-git init
-
-# Create a package.json if needed
-npm init
-
 # Install and configure if needed
-npm install --save-dev @commitlint/{config-conventional,cli}
-echo "module.exports = {extends: ['@commitlint/config-conventional']};" > commitlint.config.js
-```
-
-Alternatively the configuration can be defined in `.commitlintrc.js`, `.commitlintrc.json`, or `.commitlintrc.yml` file or a `commitlint` field in `package.json`.
-
-## First test run with Travis
-
-Add a `.travis.yml` to your project root
-
-```yaml
-# .travis.yml
-language: node_js
-before_install: git fetch --unshallow
-script:
-  - ./node_modules/.bin/commitlint --from=HEAD~1
-  - npm test
+npm install --save-dev @commitlint/travis-cli
 ```
 
-Make sure Travis is connected to your git repository.
-Trigger a build by pushing to your repository.
-
-```bash
-git add .
-git commit -m "add travis stuff"
-```
-
-We expect this build to fail:
-
-```yaml
-...
-./node_modules/.bin/commitlint --from=HEAD~1
-⧗   input: add travis stuff
-✖   message may not be empty [subject-empty]
-✖   type may not be empty [type-empty]
-✖   found 2 problems, 0 warnings
-```
-
-## Linting relevant commits
-
-What we did so far works but is not very useful as it simply lints the last commit in history.
-Let's change that by using environment information provided by TravisCI.
-
-Every build exposes the commit that triggered the build via `TRAVIS_COMMIT`.
-
-```yaml
-# .travis.yml
+```yml
+# travis.yml
 language: node_js
-before_install: git fetch --unshallow
 script:
-  - ./node_modules/.bin/commitlint --from=$TRAVIS_COMMIT
-  - npm test
-```
-
-That's a bit better, but we are not handling branches at all yet. Travis provides the branch we are on via `TRAVIS_BRANCH`.
-
-```yaml
-# .travis.yml
-language: node_js
-before_install: git fetch --unshallow
-script:
-  - ./node_modules/.bin/commitlint --from="$TRAVIS_BRANCH" --to="$TRAVIS_COMMIT"
-  - ./node_modules/.bin/commitlint --from=$TRAVIS_COMMIT
-  - npm test
-```
-
-Nice. This handles direct commits and PR originating from the same repository. Let's add forks to the mix.
-
-## The full scripts
-
-We'll have to differentiate between forks and same-repo PRs on our own and move the linting to a dedicated script.
-
-```yaml
-# .travis.yml
-language: node_js
-before_install: git fetch --unshallow
-script:
-  - /bin/bash lint-commits.sh
-  - npm test
-```
-
-```bash
-# lint-commits.sh
-#!/bin/bash
-set -e
-set -u
-
-if [[ $TRAVIS_PULL_REQUEST_SLUG != "" && $TRAVIS_PULL_REQUEST_SLUG != $TRAVIS_REPO_SLUG ]]; then
-	# This is a Pull Request from a different slug, hence a forked repository
-	git remote add "$TRAVIS_PULL_REQUEST_SLUG" "https://github.com/$TRAVIS_PULL_REQUEST_SLUG.git"
-	git fetch "$TRAVIS_PULL_REQUEST_SLUG"
-
-	# Use the fetched remote pointing to the source clone for comparison
-	TO="$TRAVIS_PULL_REQUEST_SLUG/$TRAVIS_PULL_REQUEST_BRANCH"
-else
-	# This is a Pull Request from the same remote, no clone repository
-	TO=$TRAVIS_COMMIT
-fi
-
-# Lint all commits in the PR
-# - Covers fork pull requests (when TO=slug/branch)
-# - Covers branch pull requests (when TO=branch)
-./node_modules/.bin/commitlint --from="$TRAVIS_BRANCH" --to="$TO"
-
-# Always lint the triggering commit
-# - Covers direct commits
-./node_modules/.bin/commitlint --from="$TRAVIS_COMMIT"
+  - $(npm bin)/travis-cli
 ```
 
 ?> Help yourself adopting a commit convention by using an interactive commit prompt. Learn how to use `@commitlint/prompt-cli` in the [Use prompt guide](guides-use-prompt.md)