npm start do not work in examples/js/e-commerce on windows

### 🐛 Current behavior

When running npm-start we are getting below error on windows systems
BABEL_ENV' is not recognized as an internal or external command.

Suggested fix - add **cross-env** in **package.json** has fixed the issue.

### 🔍 Steps to reproduce

go to instantsearch-master\examples\js\e-commerce
type npm install
type npm start

error - BABEL_ENV' is not recognized as an internal or external command

### Live reproduction

https://codesandbox.io/s/github/algolia/instantsearch.js/tree/templates/instantsearch.js

### 💭 Expected behavior

Server should start at port 3000

### Package version

1.15.0

### Operating system

windows

### Browser

chrome

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

Inspect examples/js/e-commerce/package.json and the npm start script first. Reproduce the issue on Windows with npm install and npm start, then verify that the example server starts on port 3000 without the BABEL_ENV error.

Written by the indexing model from the issue text.