title: Displaying a loading spinner on a map when updating with leafletProxy in Shiny
body: <p>The 'shinycssloaders' package was developed as a simple wrapper to provide loading icons to UI output, which works great.  Unfortunately, it does not work for maps that are updated via leafletProxy (only the initial map produced will use a loading icon). </p>
  
  <p>Is there a known solution for this?</p>