2.9.1

Fix startup script, anyone having used pm2 startup on the 2.9.0 version (published 10hours ago) must run:

$ npm install pm2 -g
$ pm2 update
$ pm2 unstartup
$ pm2 startup
# Command to copy/paste

bug introduced via PR 0abcfc8#diff-cd58f2bfb244d0982b2a0bf4730733bcR294