fix(ol-source-vector): handle correct event addfeature

there wa a typo before (`addFeature` instead of `addfeature`)

closes #362

Author: d-koppenhagen

src/composables/useOpenLayersEvents.ts

@@ -38,7 +38,7 @@ export const IMAGE_SOURCE_EVENTS = [
   "imageloadstart",
 ];
 export const FEATURE_EVENTS = [
-  "addFeature",
+  "addfeature",
   "changefeature",
   "clear",
   "featuresloadend",