Fix compilation when Vim path contains spaces
Fix compilation when Vim path contains spaces

g:vimtex_latexmk_progname may contain spaces so it should be
surrounded by double quotes when used in $success_cmd and
$failure_cmd latexmk options.

lervag/vimtex,Aster89/vimtex,lervag/vimtex,Aster89/vimtex,kmarius/vimtex,kmarius/vimtex