Update link to the TIFF specification

The old link is unavailable since mid-2017, so we link to archive.org

src/lib.rs

@@ -4,7 +4,7 @@
 //! lossless and lossy compression.
 //!
 //! # Related Links
-//! * <https://www.adobe.io/open/standards/TIFF.html> - The TIFF specification
+//! * <https://web.archive.org/web/20210108073850/https://www.adobe.io/open/standards/TIFF.html> - The TIFF specification
 
 extern crate jpeg;
 extern crate weezl;