版本：
文件：
- https://cdn.bootcdn.net/ajax/libs/formulajs/1.0.8/formula.js
- https://cdn.bootcdn.net/ajax/libs/formulajs/1.0.8/formula.min.js
- https://cdn.bootcdn.net/ajax/libs/formulajs/1.0.8/formula.standalone.js
- https://cdn.bootcdn.net/ajax/libs/formulajs/1.0.8/formula.standalone.min.js