Replace uniq! with uniq. Closes #258

i.e.
```irb
Loading development environment (Rails 4.1.1)
irb(main):001:0>  [].uniq!.each { |u| puts u } #               <-- uniq!
NoMethodError: undefined method `each' for nil:NilClass
	from (irb):1
	from /home/jstroop/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/railties-4.1.1/lib/rails/commands/console.rb:90:in `start'
	from /home/jstroop/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/railties-4.1.1/lib/rails/commands/console.rb:9:in `start'
	from /home/jstroop/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:69:in `console'
	from /home/jstroop/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
	from /home/jstroop/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/railties-4.1.1/lib/rails/commands.rb:17:in `<top (required)>'
	from bin/rails:4:in `require'
	from bin/rails:4:in `<main>'
irb(main):002:0>  [].uniq.each { |u| puts u } #                <-- uniq
=> []
```