not working on node v0.10.x

[yi]

node_modules/command-exists/lib/command-exists.js:13
    access(commandName, constants.F_OK,
    ^
TypeError: undefined is not a function
    at fileNotExists (/var/www/apps/wx-collector-atf-worker/shared/node_modules/command-exists/lib/command-exists.js:13:5)
    at commandExistsUnix (/var/www/apps/wx-collector-atf-worker/shared/node_modules/command-exists/lib/command-exists.js:46:5)

[mathisonian]

I'll accept a PR for this but probably won't have time to fix anytime soon