correctly set filename in windows for javascript

due to path style, routes are rendered incorrectly in windows except the first file in this case `/js/app.js`. `<%- js('app') %>`

```hml
<script src='/js\jquery.js'></script>
<script src='/templates\a1.js'></script>
<script src='/templates\a2.js'></script>
<script src='/templates\b\c.js'></script>
<script src='/js/app.js'></script>
```

This also leads to 404 not found responses for all except `/js/app.js` as they are invalid routes.

This patch replaces `\` with `/` so the scripts and routes are registered correctly.

```html
<script src='/js/jquery.js'></script>
<script src='/templates/a1.js'></script>
<script src='/templates/a2.js'></script>
<script src='/templates/b/c.js'></script>
<script src='/js/app.js'></script>
```