Keep existing target in <a>

[pierredewilde]

Flamethrower currently replaces existing link target:

<a href="https://astro.build" target="astro">

is replaced by

<a href="https://astro.build" target="_blank">

Existing target should be kept untouched.

flamethrower/lib/handlers.ts

Line 78 in 79883a4

anchor.target = '_blank';

should be replaced by

anchor.target = anchor.target || '_blank';

[nodsaibot]

might as well fork it as it will take awhile if you submit a PR