Fix timestamp to include %M instead of %I for post-deploy migrations.

lib/generators/rails/post_deployment_migration/post_deployment_migration_generator.rb

@@ -3,7 +3,7 @@ require 'rails/generators'
 module Rails
   class PostDeploymentMigrationGenerator < Rails::Generators::NamedBase
     def create_migration_file
-      timestamp = Time.now.strftime('%Y%m%d%H%I%S')
+      timestamp = Time.now.strftime('%Y%m%d%H%M%S')
 
       template "migration.rb", "db/post_migrate/#{timestamp}_#{file_name}.rb"
     end