fixes some markup issues in the js style guide docs

doc/development/fe_guide/style_guide_js.md

@@ -414,7 +414,6 @@ A forEach will cause side effects, it will be mutating the array being iterated.
 1. Default key should be provided if the prop is not required.
 _Note:_ There are some scenarios where we need to check for the existence of the property.
 On those a default key should not be provided.
-
   ```javascript
     // good
     props: {
@@ -494,7 +493,6 @@ On those a default key should not be provided.
 #### Ordering
 
 1. Tag order in `.vue` file
-
     ```
     <script>
       // ...