Potential fix for code scanning alert no. 2: Prototype-polluting function (#686)

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Author: hizzgdev

src/jsmind.util.js

@@ -74,6 +74,9 @@ export const util = {
         },
         merge: function (b, a) {
             for (var o in a) {
+                if (o === '__proto__' || o === 'constructor' || o === 'prototype') {
+                    continue;
+                }
                 if (o in b) {
                     if (
                         typeof b[o] === 'object' &&