Convert LettersService to Kotlin

Author: tuancoltech

app/src/main/java/ai/elimu/content_provider/rest/LettersService.kt

@@ -1,13 +1,10 @@
-package ai.elimu.content_provider.rest;
+package ai.elimu.content_provider.rest
 
-import java.util.List;
-
-import ai.elimu.model.v2.gson.content.LetterGson;
-import retrofit2.Call;
-import retrofit2.http.GET;
-
-public interface LettersService {
+import ai.elimu.model.v2.gson.content.LetterGson
+import retrofit2.Call
+import retrofit2.http.GET
 
+interface LettersService {
     @GET("content/letters")
-    Call<List<LetterGson>> listLetters();
+    fun listLetters(): Call<List<LetterGson>>
 }