Q: How to have plugin load conditions in TOML format?

[hasufell]

Basically, I want to translate this into toml:

if has('nvim')
  Plug 'Shougo/deoplete.nvim', { 'do': ':UpdateRemotePlugins' }
else
  Plug 'Shougo/deoplete.nvim'
  Plug 'roxma/nvim-yarp'
  Plug 'roxma/vim-hug-neovim-rpc'
endif

I know I can have conditionals in build, but I don't know how to make nvim-yarp and vim-hug-neovim-rpc only load in non-nvim in the toml file format.

[Shougo]

[[plugins]]
repo = 'Shougo/deoplete.nvim'

[[plugins]]
repo = 'roxma/nvim-yarp'
on_if = '!has("nvim")'

[[plugins]]
repo = 'roxma/vim-hug-neovim-rpc'
on_if = '!has("nvim")'

Note: :UpdateRemotePlugins is executed automatically in dein.vim