Add published_at in the seeds file

Co-authored-by: Vinicius Negrisolo <vinicius.negrisolo@hashrocket.com>
Co-authored-by: Gabriel Reis <gabriel.reis@hashrocket.com>

Author: 3 people

priv/repo/seeds.exs

@@ -33,22 +33,25 @@ developer =
     body: "A Gold Master Test in Practice",
     channel: phoenix_channel,
     developer: developer,
-    slug: Post.generate_slug()
+    slug: Post.generate_slug(),
+    published_at: DateTime.utc_now()
   })
 
   Repo.insert!(%Post{
     title: "Controlling Your Test Environment",
     body: "Slow browser integration tests are a hard problem",
     channel: elixir_channel,
     developer: developer,
-    slug: Post.generate_slug()
+    slug: Post.generate_slug(),
+    published_at: DateTime.utc_now()
   })
 
   Repo.insert!(%Post{
     title: "Testing Elixir",
     body: "A Rubyist's Journey",
     channel: erlang_channel,
     developer: developer,
-    slug: Post.generate_slug()
+    slug: Post.generate_slug(),
+    published_at: DateTime.utc_now()
   })
 end)