update pm2 so that it can be installed in node v0.11.13

Hi,

just install the new node v0.11.13

Found that pod cannot be installed because of pm2 0.7 depends on old usage module.

So, I updated the pm2. 

And seems that pm2 need to be installed with

    sudo npm install --save pm2 --unsafe-perm

Not sure how to force the --unsafe-perm in package.json. Please help