fix tablerow drop's last attribute with missing cols param

[ggmichaelgo]

When cols param is missing from the tablerow tag, tablerowloop#col_last always returns false.

Liquid template:

{% tablerow i in (1..2) %}
  {{ tablerowloop.col_last }}
{% endtablerow %}

Expected output:

<tr class="row1">
<td class="col1">
false
</td><td class="col2">
true
</td></tr>

Current output:

<tr class="row1">
<td class="col1">
false
</td><td class="col2">
false
</td></tr>

[ggmichaelgo]

ping @Shopify/guardians-of-the-liquid

[dylanahsmith]

Your PR descriptions current output is a copy of your expected output. The actual current output is

<tr class="row1">
<td class="col1">
  false
</td><td class="col2">
  false
</td></tr>

which is indeed wrong. Thanks for the fix