Update JSLoader.cpp (#29270)
Update JSLoader.cpp (#29270)

Summary:
Since react-native-cli is deprecated, the correct command should be `npx react-native start`

Pull Request resolved: https://github.com/facebook/react-native/pull/29270

Reviewed By: sammy-SC

Differential Revision: D30017028

Pulled By: sota000

fbshipit-source-id: cfcf9e1d150f51750a4e86133bd3167506ee7348

javache/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,facebook/react-native,pandiaraj44/react-native,javache/react-native,javache/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,pandiaraj44/react-native,pandiaraj44/react-native,pandiaraj44/react-native,pandiaraj44/react-native,javache/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,pandiaraj44/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,facebook/react-native,pandiaraj44/react-native,janicduplessis/react-native,facebook/react-native,pandiaraj44/react-native,janicduplessis/react-native,facebook/react-native