Fixing assets path calculation to remove trailing slash

Updating to remove the trailing slash on the assets path.
Now templates that use the assets path should use it like:
```html
<link rel="stylesheet" href="{{assets}}/css/bootstrap.css">
```
instead of:
```html
<link rel="stylesheet" href="{{assets}}css/bootstrap.css">
```

notice the / between the handlebars token and the rest of the
path to the css file.