gpa: using mirror url.

(cherry picked from commit bdc630e7e97837aa4457c7da4562f9d22e21df87)

pkgs/applications/misc/gpa/default.nix

···
   name = "gpa-0.9.7";
 
   src = fetchurl {
-    url = "ftp://ftp.gnupg.org/gcrypt/gpa/${name}.tar.bz2";
+    url = "mirror://gnupg/gpa/${name}.tar.bz2";
     sha256 = "1r8pnvfw66b2m9lhajlarbxx9172c1gzripdij01bawgbrhwp33y";
   };