Horizontal rules are incorrectly matched

[itsramiel]

Hi,

The horizontal rule regex incorrectly matches result leaving some markdown unremoved.

The current regex: https://github.com/zuchka/remove-markdown/blob/c96417bbb16a9e89dfc0b3dfafd306ad30a08867/index.js#L15

matches 3 or more -, *, _ followed by whitespace

There are two issues:

• it matches mixed symbols so, -*- or --_ but the spec mentions that the symbols need to be matching
• it matches even if there are non whitespace characters at then end of the a line something like -- -hey matches the -- - but it shouldnt according to the spec.

I came across this when having a list with a bold word in the beginning so:

- **Bold**

which wrongle matches the - ** and leaves it at Bold**. This is both case 1 and 2 from above where it matched mixing characters and also where there are nonspace characters afterwards