Bazel: update rules_pkg to v0.4.0.

Change-Id: I561d269029eca155a9a537e2b484c4f385f27365
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://nginx-review.googlesource.com/c/nginx/+/3862
Reviewed-by: Patryk Lesiewicz <patryk@google.com>

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 8417cf9..be0f060 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -30,8 +30,8 @@
 
 http_archive(
     name = "rules_pkg",
-    sha256 = "352c090cc3d3f9a6b4e676cf42a6047c16824959b438895a76c2989c6d7c246a",
-    url = "https://github.com/bazelbuild/rules_pkg/releases/download/0.2.5/rules_pkg-0.2.5.tar.gz",
+    sha256 = "038f1caa773a7e35b3663865ffb003169c6a71dc995e39bf4815792f385d837d",
+    url = "https://github.com/bazelbuild/rules_pkg/releases/download/0.4.0/rules_pkg-0.4.0.tar.gz",
 )
 
 load("@rules_pkg//:deps.bzl", "rules_pkg_dependencies")