Fix spelling mistake of the word 'kubernetes' in line 390

A volume with `volumeMode: Filesystem` is *mounted* into Pods into a directory. If the volume
is backed by a block device and the device is empty, Kubernetes creates a filesystem
on the device before mounting it for the first time.

Author: jmboby

content/en/docs/concepts/storage/persistent-volumes.md

@@ -387,7 +387,7 @@ Kubernetes supports two `volumeModes` of PersistentVolumes: `Filesystem` and `Bl
 `Filesystem` is the default mode used when `volumeMode` parameter is omitted.
 
 A volume with `volumeMode: Filesystem` is *mounted* into Pods into a directory. If the volume
-is backed by a block device and the device is empty, Kuberneretes creates a filesystem
+is backed by a block device and the device is empty, Kubernetes creates a filesystem
 on the device before mounting it for the first time.
 
 You can set the value of `volumeMode` to `Block` to use a volume as a raw block device.