sort-by-sku order printer invoice

// change line 21 from
    <th>Item</th>
// to
    <th>SKU</th>
    <th>Item</th>

// change line 30 from
    {% for line_item in line_items %}
// to
    {% assign line_items_by_sku = line_items | sort:'sku' %}
    {% for line_item in line_items_by_sku %}
    
// change line 33 from
    <td><b>{{ line_item.title }}</b></td>
// to
    <td>{{ line_item.sku }}</td>
    <td><b>{{ line_item.title }}</b></td>