Update peer dependencies

[willmcclellan]

I had an issue with the peer dependencies where and older version of leaflet would be installed on top of my applications leaflet dependency causing a mismatch between the marker file div-icon loaded and the leaflet version.

• Parent project uses leaflet 1.x.x
• react-leaflet-div-icon specifies peer dependency of 0.x.x
• when dependencies are installed, leaflet 1.x.x will be installed in root node_modules but react-leaflet-div-icon will also get leaflet 0.x.x in it's dependencies
• when react-leaflet-div-icon looks for the marker module in leaflet, it first looks its local node_modules for leaflet, which it finds and then I get an error because of module mismatch

I've updated the peer dependencies to specify the 1.x.x versions which I think should be fine because it looks like you've included updates recently to support react-leaflet's newer api and therefore the module is probably not compatible with older versions of leaflet/react-leaflet anyway