swf: Update link (ruffle-rs#8650)

The original link is not working anymore so I put a link to the wayback machine in it's place that leads to the original document

Co-authored-by: Adrian Wielgosik <[email protected]>

Author: Flawake

swf/src/types/matrix.rs

@@ -14,7 +14,7 @@ use std::ops;
 /// The SWF format uses 16.16 format for `a`, `b`, `c`, `d`. Twips are used for `tx` and `ty`.
 /// This means that objects in Flash can only move in units of twips, or 1/20 pixels.
 ///
-/// [SWF19 pp.22-24](https://www.adobe.com/content/dam/acom/en/devnet/pdf/swf-file-format-spec.pdf#page=22)
+/// [SWF19 pp.22-24](https://web.archive.org/web/20220205011833if_/https://www.adobe.com/content/dam/acom/en/devnet/pdf/swf-file-format-spec.pdf#page=22)
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct Matrix {
     /// The matrix element at `[0, 0]`. Labeled `ScaleX` in SWF19.