fix DatabaseRewinder.strategy= method

When you have `DatabaseRewinder.strategy = :truncate, only: ['foos']`,
the method `DatabaseRewinder.strategy=` seems to get an array like
`[:truncate, {:only => ['foos'}]`.
fix Cleaner#strategy= method
Except schema_migtations from chached table names

to prevent unexpected deletion
Merge pull request #11 from deeeki/except_schema_migrations

Except schema_migtations from chached table names to prevent unexpected deletion
Merge branch 'fix_strategy_assignment_method' of github.com:eitoball/database_rewinder into eitoball-fix_strategy_assignment_method

Conflicts:
	spec/database_rewinder_spec.rb
Indent :arrow_right::arrow_right: