datamash - switch download URL back to gnu.org

packages/datamash.rb

@@ -4,7 +4,7 @@ class Datamash < Package
   description 'GNU Datamash is a command-line program which performs basic numeric,textual and statistical operations on input textual data files.'
   homepage 'http://savannah.gnu.org/projects/datamash'
   version '1.2'
-  source_url 'https://mirror.sergal.org/gnu/datamash/datamash-1.2.tar.gz'
+  source_url 'https://ftpmirror.gnu.org/datamash/datamash-1.2.tar.gz'
   source_sha256 'e8d46fb22ccc77e5380f26cde622a733f363d388b04a2c22e7fb6de0e9d85996'
 
   binary_url ({