Pasting same title in html/markdown causes output to be nested #96

This is an issue that was forwarded to me, but I'm able to reproduce.

If text/html and text/plain contain the same title, the output we return is nested.

Expected output: [[Same](https://google.com/)](https://google.com)"
Actual output: [Same](https://google.com)

Reproduction: https://codepen.io/tarngerine/pen/ZEZBEpy

Try pressing the Copy button on either of the examples and try pasting into any GitHub comment box.