prefix '-n' before app name in 'copilot app show'

[davidhsingyuchen]

workshop:~/environment/ecsdemo-nodejs (main) $ copilot app show --help
Shows configuration, environments and services for an application.

Usage
  copilot app show [flags]

Flags
  -h, --help          help for show
      --json          Optional. Output in JSON format.
  -n, --name string   Name of the application.

Examples
  Shows info about the application "my-app"
  `$ copilot app show -n my-app`