change Gemfile to sorted style

* sort gems by ascii
* use sub-group style for development/test group gems

cf. https://gist.github.com/kakutani/43b9f42197ab002fcdf8
remove unused sub-group
fix Gemfile.lock
Merge pull request #203 from onk/feature/idobata_style_gemfile

change Gemfile to sorted style
cosmetic changes

* fix indentation using 2 spaces
* add or remove blank lines
* add missing spaces surrounding operator, after colon or comma
* use new hash syntax
* use def with parentheses when there are parameters
* prefer inline comments instead of block comments
* don't use `::` for method calls
Merge pull request #204 from onk/feature/cosmetic_changes

cosmetic changes
fix gems order.
Merge pull request #205 from mashiro/fix-gems-order

fix gems order.