chore: switch javascript code blocks to js

vuejs/docs@5753b78#diff-0b635f32793fe88d869035c17f5143d6a7011183741021e19963a52beb70927a

Author: naokie

src/guide/render-function.md

@@ -354,7 +354,7 @@ For the `.passive`, `.capture`, and `.once` event modifiers, they can be concate
 
 例えば:
 
-```javascript
+```js
 render() {
   return h('input', {
     onClickCapture: this.doThisInCapturingMode,