icu: init at 60.2

pkgs/development/libraries/icu/60.nix

···
+import ./base.nix {
+  version = "60.2";
+  sha256 = "065l3n0q9wqaw8dz20x82srshhm6i987fr9ync5xf9mr6n7ylwzh";
+}

pkgs/top-level/all-packages.nix

···
 
   icu58 = callPackage ../development/libraries/icu/58.nix { };
   icu59 = callPackage ../development/libraries/icu/59.nix { };
+  icu60 = callPackage ../development/libraries/icu/60.nix { };
 
   icu = icu59;