python2Packages.convertdate: fix hash

This derivation was introduced in commit
e1d60a05af55daadaeaf85d14869459b9b8c9635 with version 2.2.2 but the
sha256 hash in that commit actually corresponded to version 2.2.1,
as you can see below:

$ nix-prefetch-github --rev "v2.2.1" fitnr convertdate | jq '.sha256'
"1xgi7x9b9kxm0q51bqnmwdm5lp8vwhx5yk4d1b23r37spz9dbhw5"

pkgs/development/python-modules/convertdate/2.2.x.nix

···
     owner = "fitnr";
     repo = pname;
     rev = "v${version}";
-    sha256 = "1xgi7x9b9kxm0q51bqnmwdm5lp8vwhx5yk4d1b23r37spz9dbhw5";
+    sha256 = "07x1j6jgkmrzdpv2lhpp4n16621mpmlylvwdwsggdjivhzvc3x9q";
   };
 
   propagatedBuildInputs = [