Minor refactor - uses enumerable#to_a instead of iterate and add to an array

It is just a minor refactor to make the code clear. The [Enumerable#to_a](http://ruby-doc.org/core-2.0/Enumerable.html#method-i-to_a) do the same job as the iteration + array addition.

I also take to the opportunity to remove [some white spaces](https://github.com/phstc/rails/compare/minor-refactor-code-gardener-grouping?expand=1#L2L122) and one [unnecessary empty line](https://github.com/phstc/rails/compare/minor-refactor-code-gardener-grouping?expand=1#L3L238).