Clean styles by Rubocop

[nard-tech]

Clean styles by Rubocop.

All tests were passed.

[nard-tech]

@james2m TravisCI is failed in Ruby 2.3 due to this error.

$ bundle install --jobs=3 --retry=3
The dependency activerecord-jdbcsqlite3-adapter (~> 1.3.25) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for java. To add those platforms to the bundle, run `bundle lock --add-platform java`.
Fetching gem metadata from http://rubygems.org/..........
Fetching gem metadata from http://rubygems.org/.
Resolving dependencies...
Bundler could not find compatible versions for gem "bundler":
  In rake10.gemfile:
    bundler (~> 1.11)
  Current Bundler version:
    bundler (2.0.1)
This Gemfile requires a different version of Bundler.
Perhaps you need to update Bundler by running `gem install bundler`?
Could not find gem 'bundler (~> 1.11)' in any of the relevant sources:
  the local ruby installation
The command "eval bundle install --jobs=3 --retry=3 " failed. Retrying, 2 of 3.