'ExcelApi.js' is missing

In versions above `1.2.0`, `main.js` has a line in it:

```
fin.desktop.Excel = require('./ExcelApi.js').LegacyApi;
```

but it seems that `ExcelApi.js` file is missing in `src/`.  Although version `1.0.1` has it in the root folder of the repo: https://github.com/openfin/excel-api-example/tree/1.0.1
