p4: 2020.1.1991450 -> 2020.1.2007551

The download URL hasn't changed, but the sha256 and user facing download
version has. See [perforce downloads][p4-download].

[p4-download]: https://www.perforce.com/downloads/helix-command-line-client-p4

pkgs/applications/version-management/p4/default.nix

···
 
 stdenv.mkDerivation rec {
   pname = "p4";
-  version = "2020.1.1991450";
+  version = "2020.1.2007551";
 
   src = fetchurl {
     url = "https://cdist2.perforce.com/perforce/r20.1/bin.linux26x86_64/helix-core-server.tgz";
-    sha256 = "0nhcxhwx3scx6vf7i2bc8j0b1l57lmq9bfy1cfbfbqasd3an721k";
+    sha256 = "0ly9b838zrpp6841fzapizdd3xmria55bwfrh2j29qwxiwzqj80y";
   };
 
   sourceRoot = ".";