Change localizely format to json

localizely.yml

@@ -1,6 +1,6 @@
 config_version: 1.0
 project_id: ead34689-ec52-41d9-b675-09bc85a6cbd7
-file_type: flutter_arb
+file_type: json
 upload:
   files:
     - file: mobile/assets/i18n/en-US.json
@@ -12,4 +12,4 @@ download:
     - file: mobile/assets/i18n/en-US.json
       locale_code: en
     - file: mobile/assets/i18n/de-DE.json
-      locale_code: de
+      locale_code: de