Enable tree shaking for leaflet

package.json

@@ -5,7 +5,8 @@
   "scripts": {
     "serve": "vue-cli-service serve ",
     "build": "vue-cli-service build --report",
-    "lint": "vue-cli-service lint"
+    "lint": "vue-cli-service lint",
+    "postinstall": "node --experimental-modules --experimental-json-modules scripts/fix-leaflet.mjs"
   },
   "dependencies": {
     "core-js": "^3.6.5",

scripts/fix-leaflet.mjs

@@ -0,0 +1,11 @@
+// @ts-check
+import pkgJson from '../node_modules/leaflet/package.json';
+
+import { writeFileSync } from 'fs';
+
+writeFileSync(
+  './node_modules/leaflet/package.json',
+  JSON.stringify({
+    ...pkgJson,
+    module: 'dist/leaflet-src.esm.js',
+  }, null, 2));