Corrected the field names in the secret

Author: talonx

content/en/docs/tasks/configmap-secret/managing-secret-using-kubectl.md

@@ -105,8 +105,8 @@ Type:            Opaque
 
 Data
 ====
-password.txt:    12 bytes
-username.txt:    5 bytes
+password:    12 bytes
+username:    5 bytes
 ```
 
 The commands `kubectl get` and `kubectl describe` avoid showing the contents