Allows you to override the root path directly on a per-instance basis

[nathanpalmer]

This helps in situations where you are creating or updating views from within a Rails engine. By adding the root_path to the statement it will be able to correctly find the file.

The , root_path: Database::Engine.root is the part that is manually added. I didn't find any method of autodetecting the rails engine so this would have to be manually added after generating the migration.

Solves the issue I brought up in #261

create_view

create_view :product_stats, version: 2, root_path: Database::Engine.root

update_view

update_view :product_stats, version: 2, revert_to_version: 1, root_path: Database::Engine.root

replace_view

replace_view :product_stats, version: 2, revert_to_version: 1, root_path: Database::Engine.root