protobuf: 3.15.1 -> 3.15.2

https://github.com/protocolbuffers/protobuf/releases/tag/v3.15.2

pkgs/development/libraries/protobuf/3.15.nix

@@ -1,6 +1,6 @@
 { callPackage, ... }:
 
 callPackage ./generic-v3.nix {
-  version = "3.15.1";
-  sha256 = "0rxl0vkv532x85q9cf11njw12vmp9kxqb1i8hdg4lfmi55waa9wr";
+  version = "3.15.2";
+  sha256 = "12da2h5ds8yjyssqansvhd2vy72kw6b60j9l6va21ghs8xzyihqi";
 }