Fix internal links in PDF export

This release fixes internal links when exporting a markdown note into PDF format.

Previously, internal links were rendered unclickable when exporting a note as a PDF. This issue was caused by accessing the .opacity property when defining .md-def-url properties. Access to that property has been removed and internal links should work again after exporting!

Thank you to @sunkoto for bringing this issue up in #19 ❤️