Update to kotlin syntax highlighting

docs/docs/v4/image-coil/README.md

@@ -4,7 +4,7 @@
 
 Image loading based on `Coil` library
 
-```kt
+```kotlin
 val markwon = Markwon.builder(context)
         // automatically create Coil instance
         .usePlugin(CoilImagesPlugin.create(context))
@@ -32,4 +32,4 @@ val markwon = Markwon.builder(context)
             }
         }, customImageLoader))
         .build()
-```
+```