Update babel7 to the latest version 🚀 (#751)

* chore(package): update @babel/core to version 7.4.0

* chore(package): update @babel/plugin-proposal-class-properties to version 7.4.0

* chore(package): update @babel/plugin-transform-flow-comments to version 7.4.0

* chore(package): update @babel/plugin-transform-flow-strip-types to version 7.4.0

* chore(package): update @babel/plugin-transform-runtime to version 7.4.0

* chore(package): update @babel/polyfill to version 7.4.0

* chore(package): update @babel/preset-env to version 7.4.0

* chore(package): update @babel/runtime to version 7.4.0

* chore(package): update lockfile package-lock.json

Author: greenkeeper[bot]