chore: enable Greenkeeper 🌴 (#7602)

* chore(package): update dependencies

* chore(travis): whitelist greenkeeper branches

* docs(readme): add Greenkeeper badge

* chore(package): Revert package.json changes

Just want to merge this so Greenkeeper gets enabled

.travis.yml

@@ -11,6 +11,7 @@ branches:
   only:
   - master
   - v3
+  - /^greenkeeper/.*$/
 
 env:
   global:

README.md

@@ -10,6 +10,7 @@
 ![node](https://img.shields.io/node/v/sequelize.svg)
 [![License](https://img.shields.io/npm/l/sequelize.svg?maxAge=2592000?style=plastic)](https://github.com/sequelize/sequelize/blob/master/LICENSE)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)
+[![Greenkeeper badge](https://badges.greenkeeper.io/sequelize/sequelize.svg)](https://greenkeeper.io/)
 
 Sequelize is a promise-based Node.js ORM for Postgres, MySQL, SQLite and Microsoft SQL Server. It features solid transaction support, relations, read replication and more.