JS: function-assigned-to-variable unnecessary space after `function`

```js
const g = function (){}
//    ^ entity.name.function.js.fjsx15
const h = function() {}
//    ^ variable.other.readwrite.js.fjsx15
```

https://github.com/borela/naomi/blob/68b4f0bd555ab98d370a9d27e4b4df675b4813c8/syntaxes/fjsx15/variable.sublime-syntax#L183

```diff
-          function\s
+          function\b
```