only init ycm extension, when YCM is available
only init ycm extension, when YCM is available

chrisbra/vim-airline,tschundler/dotfiles,tschundler/dotfiles,HarmtH/vim-airline,tschundler/dotfiles,yzhou61/vim-airline,sappo/vim-airline,wilywampa/vim-airline,bling/vim-airline,vim-IDE/vim-airline,dalguji/vim-airline,unphased/vim-airline,mildred/vim-airline,rchicoli/vim-airline,blueyed/vim-airline