Bring app in line with Hanami 2.1.0 base

app/relations/post_trips.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Adamantium
+  module Relations
+    class PostTrips < ROM::Relation[:sql]
+      schema :post_trips, infer: true do
+        associations do
+          belongs_to :post
+          belongs_to :trip
+        end
+      end
+
+      auto_struct(true)
+    end
+  end
+end