(maint) Generate changelog from v4.13.0

The GitHub Changelog Generator, which is used for release preparation,
is getting rate limited by GitHub when seraching through pull requests
and issues.

This commit sets GHCLG to start from the last release, v4.13.0.

Author: mhashizume

.sync.yml

@@ -58,4 +58,4 @@ spec/default_facts.yml:
 spec/spec_helper.rb:
   unmanaged: true
 Rakefile:
-  changelog_since_tag: 'v4.12.1'
+  changelog_since_tag: 'v4.13.0'

Rakefile

@@ -50,7 +50,7 @@ if Bundler.rubygems.find_name('github_changelog_generator').any?
     raise "Set CHANGELOG_GITHUB_TOKEN environment variable eg 'export CHANGELOG_GITHUB_TOKEN=valid_token_here'" if Rake.application.top_level_tasks.include? "changelog" and ENV['CHANGELOG_GITHUB_TOKEN'].nil?
     config.user = "#{changelog_user}"
     config.project = "#{changelog_project}"
-    config.since_tag = "v4.12.1"
+    config.since_tag = "v4.13.0"
     config.future_release = "#{changelog_future_release}"
     config.exclude_labels = ['maintenance']
     config.header = "# Change log\n\nAll notable changes to this project will be documented in this file. The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](http://semver.org)."