fix indentation of the generated files

update from 4 to 2
Note that seeds.rb only generated in development
Merge pull request #10 from binaryphile/master

Note that seeds.rb only generated in development
Merge pull request #9 from dmitry/master

Fix indentation of the generated files
fix minor wording issue in generated seeds.rb
Merge pull request #11 from binaryphile/wording

fix minor wording issue in generated seeds.rb
Autoload SeedMigration::DataMigration

That fixes #12
Add specs for threadsafe environment