Update method creation syntax to ES6 `IconSet.js`

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• [ ] 📝 Update the file \src/iconsets/IconSet.js in the Leaflet.DistortableImage repository (press the little pen Icon) and edit the line as shown below.

@@ -6,12 +6,12 @@ L.IconSet = L.Class.extend({

   _symbols: '',

-  render: function() {
+  render() {
     this.addSymbols(this._symbols);
     return this._svg;
   },

-  addSymbols: function(symbols) {
+  addSymbols(symbols) {
     this._svg += symbols;
   },
 });

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[TildaDares]

Reserved for @Khadeeejah for 24 hours!