Updating d/watch as upstream now uses Github

debian/changelog

+libfastutil-java (8.4.4-2) UNRELEASED; urgency=medium
+
+  * Updating d/watch as upstream now uses Github
+
+ -- Pierre Gruet <pgt@debian.org>  Tue, 30 Mar 2021 10:46:06 +0200
+
 libfastutil-java (8.4.4-1) unstable; urgency=medium
 
   * New upstream version 8.4.4

debian/watch

 version=4
-http://fastutil.di.unimi.it/fastutil-([.\d]+)-src\.tar\.gz
+https://github.com/vigna/fastutil/tags (?:.*?/)?v?(\d[\d.]*)\.tar\.gz