Add yarn resolution to avoid multiple versions of leaflet

frontend/README.md

@@ -92,7 +92,10 @@ Development
 Build it yourself
 -----------------
 
-Make sure to have yarn installed. Install the dependencies using `yarn run deps` and bundle the JavaScript
+Make sure to have the newest version of yarn installed. `package.json` uses resolutions, which are only supported by
+recent versions of yarn.
+
+Install the dependencies using `yarn run deps` and bundle the JavaScript
 by running `yarn run build`.
 
 A better way to develop the frontend is to start facilmap-server in dev mode. It will set up a webpack-dev-server that

frontend/package.json

@@ -85,5 +85,8 @@
     "unzipper": "^0.8.4",
     "url-loader": "^0.5.7",
     "webpack": "^2.2.1"
+  },
+  "resolutions": {
+    "**/leaflet": "1.0.3"
   }
 }

frontend/yarn.lock

@@ -2769,7 +2769,7 @@ leaflet.markercluster@^1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/leaflet.markercluster/-/leaflet.markercluster-1.0.3.tgz#64c779365c0951f4885c3414024a994f3effc708"
 
-leaflet@>=0.7.0, leaflet@^0.7.3, leaflet@^1.0.3:
+leaflet@1.0.3, leaflet@>=0.7.0, leaflet@^0.7.3, leaflet@^1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/leaflet/-/leaflet-1.0.3.tgz#1f401b98b45c8192134c6c8d69686253805007c8"