gen-release-note.rb: Avoid to depend release metadata

Because it doesn't have metadata when I edit draft.

tool/releng/gen-release-note.rb

@@ -1,6 +1,7 @@
 #!/usr/bin/env ruby
-require "open-uri"
-require "yaml"
+require 'open-uri'
+require 'time'
+require 'yaml'
 
 # Confirm current directory is www.ruby-lang.org's working directory
 def confirm_w_r_l_o_wd
@@ -11,8 +12,6 @@ def confirm_w_r_l_o_wd
 end
 confirm_w_r_l_o_wd
 
-releases = YAML.load_file('_data/releases.yml')
-
 %w[
     https://hackmd.io/@naruse/ruby-relnote-en/download
     https://hackmd.io/@naruse/ruby-relnote-ja/download
@@ -28,18 +27,10 @@ releases = YAML.load_file('_data/releases.yml')
   end
   puts "#{url} -> #{version}"
 
-  release = releases.find{|rel|rel['version'] == version}
-  unless release
-   abort "#{version} is not found in '_data/releases.yml'"
-  end
 
   # Write release note article
-  lang = url[/ja|en/]
-  if %r<\A/en/news/(\d+/\d+/\d+/ruby-[\w\-]+-released)> =~ release['post']
-    path = "#{lang}/news/_posts/#{$1.tr('/', '-')}.md"
-  else
-    abort "unexpected path pattern '#{release['post']}'"
-  end
+  path = Time.parse(src[/^date: (.*)/, 1]).
+    strftime("./#{src[/^lang: (\w+)/, 1]}/news/_posts/%Y-%m-%d-ruby-#{version}-released.md")
   puts path
   File.write(path, src)
 end