Feature/122 add optional drag step prop (#125)

* added a dragStep prop that mimics the logic of the step prop but only for drag/swipe events

* Fixed the tests that I foolishly broke

* fixed package-lock, rollup config, and a linting error

* updated readme and typings to include drag step

* filtered dragStep from CarouselProvider props

* Updated all build files

* added dragStep into componentWillReceiveProps updating the store state

* ran the build

Author: littlejustinh

dist/index.cjs.js

@@ -105,6 +105,7 @@ const CarouselProvider = class CarouselProvider extends React.Component {
       'orientation',
       'playDirection',
       'step',
+      'dragStep',
       'totalSlides',
       'touchEnabled',
       'dragEnabled',