Add bundle update command to Bundler installation instructions

hsbt · hsbt · commit 2953c5dd124e · 2025-11-26T13:20:30.000+09:00
diff --git a/Rakefile b/Rakefile
@@ -397,6 +397,7 @@ To update to the latest RubyGems you can run:
 To update to the latest Bundler you can run:
 
     gem install bundler [--pre]
+    bundle update --bundler=#{v}
 
 ## RubyGems Release Notes
 
