Trim trailing line to ensure empty toc is empty

[Krinkle]

Use case:

{%- if include.toc -%}
	{%- capture jekyll_toc -%}{%- include toc.html html=content -%}{%- endcapture -%}
	{%- if jekyll_toc != '' -%}
		<div class="toc-wrapper">
		<h4>Table of contents</h4>{{ jekyll_toc }}</div>
	{%- endif -%}
{%- endif -%}

It is also possible to store the toc.html layout file in the Git repository without trailing newline. However, when copying it into other projects this is often not preserved since trailing newline at EOF is a commonly enforced convention by various tooling, including Git itself, and in text editors when merely opening the file to e.g. copy/paste the latest version.

[allejo]

Thank you for the PR! I've tagged a minor release of v1.2.0 since using whitespace control requires Jekyll 3.5+.