react-dates

[test] transform modules in karma so sinon can stub properly

[Dev Deps] update `@babel/cli`, `@babel/core`, `@babel/register`, `acorn`, `airbnb-js-shims`, `aphrodite`, `babel-loader`, `babel-plugin-inline-react-svg`, `babel-plugin-istanbul`, `babel-preset-airbnb`, `coveralls`, `enzyme`, `enzyme-adapter-react-helper`, `eslint`, `eslint-plugin-import`, `eslint-plugin-jsx-a11y`, `eslint-plugin-react`, `node-sass`, `rimraf`, `sinon`, `webpack`

Version 20.2.0

[New] `CalendarMonth`: Pass isVisible to renderMonthElement

Merge pull request #1578 from GattoLupesco/fix_singledatepicker_focus_on_ie11