Fix Ruby 2.1 warnings

Fixes following Ruby warnings:

> gems/ruby-2.1.2/gems/semantic-1.3.0/lib/semantic/version.rb:81: warning: ambiguous first argument; put parentheses or even spaces
> gems/ruby-2.1.2/gems/semantic-1.3.0/lib/semantic/version.rb:108: warning: `&' interpreted as argument prefix