tests: add extra kitchensink test

Author: MichaelDeBoey

src/__tests__/__fixtures__/kitchensink.md

@@ -17,6 +17,8 @@ This is a paragraph with a [link](https://example.com).
 
 [](https://example.com)
 
+https://example.com
+
 https://codepen.io/team/codepen/pen/PNaGbb
 
 https://codesandbox.io/s/ynn88nx9x?view=split

src/__tests__/plugin.js

@@ -48,6 +48,7 @@ describe('gatsby-remark-embedder', () => {
       <p><a href="https://example.com" title="A link to example.com">https://example.com</a></p>
       <p><a href="https://example.com">https://example.com</a></p>
       <p><a href="https://example.com"></a></p>
+      <p>https://example.com</p>
       <iframe src="https://codepen.io/team/codepen/embed/preview/PNaGbb" style="width:100%; height:300px;"></iframe>
       <iframe src="https://codesandbox.io/embed/ynn88nx9x?view=split" style="width:100%; height:500px; border:0; border-radius: 4px; overflow:hidden;" allow="accelerometer; ambient-light-sensor; camera; encrypted-media; geolocation; gyroscope; hid; microphone; midi; payment; usb; vr; xr-spatial-tracking" sandbox="allow-forms allow-modals allow-popups allow-presentation allow-same-origin allow-scripts"></iframe>
       <div style="width:100%;height:0;padding-bottom:63%;position:relative;"><iframe src="https://giphy.com/embed/XatG8bioEwwVO" width="100%" height="100%" style="position:absolute" frameborder="0" class="giphy-embed-from-cache" allowfullscreen></iframe></div>