add migration to increase links url size (#683)

lib/postal/message_db/migrations/19_increase_links_url_size.rb

@@ -0,0 +1,11 @@
+module Postal
+  module MessageDB
+    module Migrations
+      class IncreaseLinksUrlSize < Postal::MessageDB::Migration
+        def up
+          @database.query("ALTER TABLE `#{@database.database_name}`.`links` MODIFY `url` TEXT")
+        end
+      end
+    end
+  end
+end