modify .vimrc

ref. https://github.com/rhysd/dotfiles/blob/7faa1e5b83788bdc8b67462e23479cc285b8ab6b/vimrc#L200-201
modify .vimrc

ref. https://github.com/rhysd/dotfiles/blob/7faa1e5b83788bdc8b67462e23479cc285b8ab6b/vimrc#L204-205