Update nginx maintainer signer key list

See paketo-buildpacks/nginx#740

tasks/build-binary-new-cflinuxfs4/builder.rb

@@ -132,8 +132,8 @@ module DependencyBuildHelper
   class << self
     def build_nginx_helper(source_input, custom_options, static = false)
       public_gpg_key_urls = [
-        "http://nginx.org/keys/mdounin.key", # Maxim Dounin’s PGP public key
         "http://nginx.org/keys/maxim.key", # Maxim Konovalov’s PGP public key
+        "http://nginx.org/keys/arut.key", # Roman Arutyunyan's PGP public key
         "https://nginx.org/keys/pluknet.key", # Sergey Kandaurov’s PGP public key
         "http://nginx.org/keys/sb.key", # Sergey Budnevitch’s PGP public key
         "http://nginx.org/keys/thresh.key", # Konstantin Pavlov’s PGP public key