* Add map prop/option `transformRequest`.
* Upgrade sinon package to webpack-compatible version.
* Fix test for map onLoad prop.
* Add test for new Map prop `transformRequest`.
* Document and cleanup new `tranformRequest` prop on Map component.
Switch around the Latitude and Longitude values in the example (for ReactMapGL and Marker). The current values are not a proper LatLng pair, and PerspectiveMercatorViewport.project() returns NaN values.