update documentation with new kaniko version

Author: kuuji

docs/pages/configuration/images/kaniko.mdx

@@ -142,7 +142,7 @@ The `image` option expects a string stating the image that should be used for th
 
 #### Default Value For `image`
 ```yaml
-image: gcr.io/kaniko-project/executor:v0.17.1
+image: gcr.io/kaniko-project/executor:v1.8.1
 ```
 
 #### Example: Use Different Kaniko Image/Version
@@ -152,7 +152,7 @@ images:
     image: 123.456.789.0:5000/john/appbackend
     build:
       kaniko:
-        image: gcr.io/kaniko-project/executor:v0.19.0
+        image: gcr.io/kaniko-project/executor:v1.6.0
 ```
 
 ### `initImage`