Add ignore_create_seed_file option
Rename ignore_create_seed_file to update_seeds_file
Add spec for SeedMigration.update_seeds_file
Improved conditios
Remove seeds.rb if exists(when update_seeds_file is false context)
Add spec for checking doesn't update seeds.rb
Merge pull request #20 from ukstudio/ignore_create_seed_file

Add ignore_create_seed_file option