chore(package): update react-docgen to version 2.2.0
chore(package): update react-docgen to version 2.2.0

http://greenkeeper.io/
sapegin/react-styleguidist,cgvarela/react-styleguidist,panayi/react-styleguidist,sourcejs/sourcejs-react-styleguidist,styleguidist/react-styleguidist,sapegin/react-styleguidist,styleguidist/react-styleguidist,styleguidist/react-styleguidist,sourcejs/sourcejs-react-styleguidist,cgvarela/react-styleguidist,bluetidepro/react-styleguidist,psachs21/react-styleguidist,panayi/react-styleguidist