Multiline subtitles

[frost768]

First of all thanks for this great library and conversion to typescript.
The problem is that the regex in vtt doesn't capture the first line of a multiline subtitle.
For example:

WEBVTT

00:00:00.000 --> 00:00:10.000 position:45%,line-right align:center size:35%
- Hey
- Hi

00:00:11.000 --> 00:00:20.000
- Hey
- Hi

The first caption's output is '-Hey -Hi' but the second one's is just '- Hi'.
I believe it is related to \s?.*\r?\n regex before the text group ([\s\S]*).
It matches with the first line and completely disregards it.
Explanation:
In the first caption;

• `\s?' matches with the space between the times and style
• .*\r?\n matches with the style and the new line

In the second caption;

• `\s?' doesn't match anything because there is no space
• .*\r?\n matches with - Hey because it takes every character until it comes across with a new line which also happens to be the first line of the caption.

https://github.com/leranjun/subsrt-ts/blob/862a66da48ef883b328ae6ceb5e3b4627fed5f5c/lib/format/vtt.ts#L40-L42