fix(runtime-dom): fix patching for attributes starting with on

fix #949

BREAKING CHANGE: Only props starting with `on` followed by an uppercase
letter or a non-letter character are considered event listeners.

packages/runtime-core/src/componentEmits.ts

@@ -66,12 +66,12 @@ export function emit(
     }
   }
 
-  let handler = props[`on${event}`] || props[`on${capitalize(event)}`]
+  let handler = props[`on${capitalize(event)}`]
   // for v-model update:xxx events, also trigger kebab-case equivalent
   // for props passed via kebab-case
   if (!handler && event.indexOf('update:') === 0) {
     event = hyphenate(event)
-    handler = props[`on${event}`] || props[`on${capitalize(event)}`]
+    handler = props[`on${capitalize(event)}`]
   }
   if (handler) {
     callWithAsyncErrorHandling(