As Blake correctly stated, there is no configuration file on the switches. Unlike a 'traditional' switch the Meraki switches are completely cloud managed. Yes, they do obtain (download) a configuration from the Meraki cloud - they obviously have to to be able to operate - but its not a configuration that is readable, or can be extracted from the switch.
If you're looking to take a backup (snapshot in time) that you can keep then what is available through the Dashboard is essentially the current configuration (unless you've made any changes in the last couple of minutes that haven't made their way to the switch). You can access most of this configuration through the Dashboard API, and I'm sure there are some scripts out there (e.g. on Git Hub) that do exactly this.
If you're looking to ensure that there is a backup of the configuration in case the switch fails then you don't need to, that's one of the great things about Meraki - the configuration is held in the Dashboard. And just for comfort there are two copies of your shard (essentially where your Dashboard is stored) in a primary Data Centre for your region, and a third in a secondary Data Centre in your region... so you should never be without your configuration through the Dashboard.