He linked to his vimrc on github from the article. The binding is done in this block:
if has("gui_macvim") "Use Experimental Renderer option must be enabled for transparencY
set transparency=15
set guifont=Monaco:h10
set noantialias " I like my Monaco this way ;D
" Swipe to move between bufers :D
map <SwipeLeft> :bprev<CR>
map <SwipeRight> :bnext<CR>
endif
