Prefer local repo install of eslint over global install with neomake
Thanks to @mtscout6 for the syntastic version as inspiration, and @ohjames for performance improvements.
Using vim plugged you just need to add the following to your vimrc:
Plug 'benjie/neomake-local-eslint.vim'
Then open vim and run :PlugInstall
Inspired by http://blog.pixelastic.com/2015/10/05/use-local-eslint-in-syntastic/