fix degrade in translation

fix degraded translate file error introduced in #43.

/opt/vagrant/embedded/gems/gems/i18n-0.6.4/lib/i18n/backend/base.rb:180:in `rescue in load_yml': can not load translations from /home/miurahr/.vagrant.d/gems/gems/vagrant-kvm-0.1.3/locales/en.yml: #<Psych::SyntaxError: (/home/miurahr/.vagrant.d/gems/gems/vagrant-kvm-0.1.3/locales/en.yml): found a tab character where an intendation space is expected while scanning a block scalar at line 6 column 26> (I18n::InvalidLocaleData)