build(ci): releasing with rultor

Author: rultor

.rultor.yml

@@ -3,10 +3,26 @@ docker:
   as_root: true
 architect:
   - rafamizes
+assets:
+  credentials.json: rafamizes/secret#assets/publishing/flutter/credentials.json
 merge:
-  script:
-    - flutter clean
-    - flutter pub get
-    - flutter test --no-pub
-    - flutter pub publish --dry-run
   squash: true
+  rebase: true
+  script: |
+    flutter clean
+    flutter pub get
+    flutter test --no-pub
+    flutter pub publish --dry-run
+release:
+  # updates pubspec.yaml's version attribute to $tag;
+  # in CHANGELOG, places section '[$tag] - YYYY-mm-dd' under [Unreleaded];
+  # commits the $tag version and publishes to pub.dev;
+  # Rultor tags the lastest commit as $tag and push the new tag to the
+  # repository.
+  script: |-
+    sed -i "s/^\(version:\).*/\1 $tag/" pubspec.yaml
+    sed -i "/\[Unreleased\]/a\\\n## [$tag] - $(date '+%F')" CHANGELOG.md
+    git commit -am "version $tag"
+    mkdir -p ~/.pub-cache
+    mv ../credentials.json ~/.pub-cache/credentials.json
+    flutter pub publish -f

CHANGELOG.md

@@ -5,8 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
-### Added
-- read-only master branch with [rultor](http://www.rultor.com/)
+### Changed
+- read-only master branch with [rultor](http://www.rultor.com/).
+- automate releasing with rultor.
 
 ## [0.2.5+2] - 2021-04-29
 ### Fixed