Expose essential CSS in package.json style attr (fixes #906)
Expose essential CSS in package.json style attr (fixes #906)

The `style` attribute is useful when using `Leaflet.markerCluster` with most node bundling systems (e.g. Browserify, Webpack) or any setup that uses PostCSS.

Note - only one of the two CSS files is exposed with this change. The `package.json` `style` attribute doesn't have a standardised behaviour but in the most popular implementations accepts only a string (as opposed to an array of strings). There are two css files shipped with `Leaflet.markerCluster`, only [`MarkerCluster.css`](https://github.com/Leaflet/Leaflet.markercluster/blob/master/dist/MarkerCluster.css) is essential (`MarkerCluster.Default.css` is only needed for some use-cases).
ghybs/Leaflet.markercluster,Leaflet/Leaflet.markercluster,Leaflet/Leaflet.markercluster,ghybs/Leaflet.markercluster