fix(proxy-state-tree): ensure object is extensible to identify as class

Author: christianalfoni

packages/node_modules/proxy-state-tree/src/Proxyfier.ts

@@ -21,7 +21,7 @@ const arrayMutations = new Set([
 const getValue = (proxyOrValue) =>
   proxyOrValue && proxyOrValue[IS_PROXY] ? proxyOrValue[VALUE] : proxyOrValue
 
-const isClass = (value) => typeof value === 'object' && value !== null && !Array.isArray(value) && value.constructor.name !== 'Object'
+const isClass = (value) => typeof value === 'object' && value !== null && !Array.isArray(value) && value.constructor.name !== 'Object' && Object.isExtensible(value)
 
 const getArrayMutationRevert = (method: string, target: any[], args: any[]) => {
   switch (method) {