mailto: links don't work

[legal90]

Hi!
It regression of #46

Reproduced on docsify-cli 4.2.1:

# Source:
[My Name](mailto:my@email.com)

# Renders to:
<a href="mailto:my@email.com" target="_blank">My Name</a>

The link doesn't work because of target="_blank". If you click it will just open an empty tab, not an e-mail application.

# Source:
<my@email.com>

# Renders to: 
<a href="#/97;ilto:my@email.com">my@email.com</a>

The link is just broken.