Use `ActiveRecord::Tasks::DatabaseTasks.structure_dump` instead of `ActiveRecord::Base.connection.structure_dump`, fixes `ar:structure:dump`
Small refactoring
Merge pull request #1608 from padrino/fix-structure-sql

Use `ActiveRecord::Tasks::DatabaseTasks.structure_dump` instead of `ActiveRecord::Base.connection.structure_dump`, fixes `ar:structure:dump`