replace t.has_attached_file with t.attachment as the former is deprecated and throws a warning.

lib/generators/paperclip/templates/paperclip_migration.rb.erb

@@ -2,7 +2,7 @@ class <%= migration_class_name %> < ActiveRecord::Migration
   def self.up
     change_table :<%= table_name %> do |t|
 <% attachment_names.each do |attachment| -%>
-      t.has_attached_file :<%= attachment %>
+      t.attachment :<%= attachment %>
 <% end -%>
     end
   end

test/generator_test.rb

@@ -20,7 +20,7 @@ class GeneratorTest < Rails::Generators::TestCase
           assert_class_method :up, migration do |up|
             expected = <<-migration
               change_table :users do |t|
-                t.has_attached_file :avatar
+                t.attachment :avatar
               end
             migration
 
@@ -50,8 +50,8 @@ class GeneratorTest < Rails::Generators::TestCase
           assert_class_method :up, migration do |up|
             expected = <<-migration
               change_table :users do |t|
-                t.has_attached_file :avatar
-                t.has_attached_file :photo
+                t.attachment :avatar
+                t.attachment :photo
               end
             migration