```ruby
class GitClient
  def last_commit_message(dir)
    Dir.chdir(dir) { `git log --format=%B -n 1 HEAD` }
  end
end
```

Make last_commit_message a class method of GitClient
user
```ruby
class GitClient
  def self.last_commit_message(dir)
    Dir.chdir(dir) { `git log --format=%B -n 1 HEAD` }
  end
end
```
assistant