Remove trailing space in Swig item template to enhance syntax highlighting

The space between the name of a `@function` / `@mixin` and the opening parentheses causes Prism to choke / not recognize and highlight everything correctly.

__Before:__
```scss
@mixin name () { ... }
@function name () { ... }
```

This caused Prism to not highlight everything correctly like so:

```html
<code class=" language-scss" data-language="scss">
  <span class="token keyword">@mixin</span> text-highlighted ()<span class="token selector"> </span><span class="token punctuation">{</span> ... <span class="token punctuation">}</span>
</code>
```

__After:__

```scss
@mixin name() { ... }
@function name() { ... }
```

Which results in correctly formatted markup via prism:

```html
<code class=" language-scss" data-language="scss">
  <span class="token keyword">@mixin</span> <span class="token function">text-highlighted</span>()<span class="token selector"> </span><span class="token punctuation">{</span> ... <span class="token punctuation">}</span>
</code>
```