font-manager: use the authoritative repo name

the old repo <https://github.com/FontManager/master> just redirects to
<https://github.com/FontManager/font-manager>.

pkgs/applications/misc/font-manager/default.nix

···
 
   src = fetchFromGitHub {
     owner = "FontManager";
-    repo = "master";
+    repo = "font-manager";
     rev = version;
-    sha256 = "sha256-M13Q9d2cKhc0tudkvw0zgqPAFTlmXwK+LltXeuDPWxo=";
+    hash = "sha256-M13Q9d2cKhc0tudkvw0zgqPAFTlmXwK+LltXeuDPWxo=";
   };
 
   nativeBuildInputs = [