Added addressable to gemspec.

Added 'addressable' gem to the dependencies to prevent rails from crashing.

```
/Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require': cannot load such file -- addressable/uri (LoadError)
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/barometer-0.9.0/lib/barometer/utils/address.rb:1:in `<top (required)>'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/barometer-0.9.0/lib/barometer/utils.rb:14:in `require_relative'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/barometer-0.9.0/lib/barometer/utils.rb:14:in `<top (required)>'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/barometer-0.9.0/lib/barometer.rb:2:in `require_relative'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/barometer-0.9.0/lib/barometer.rb:2:in `<top (required)>'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `block (2 levels) in require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `each'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `block in require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `each'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247@global/gems/bundler-1.3.5/lib/bundler.rb:132:in `require'
	from /Users/jim/Sites/camm-app-html/config/application.rb:7:in `<top (required)>'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/railties-3.2.13/lib/rails/commands.rb:39:in `require'
	from /Users/jim/.rvm/gems/ruby-2.0.0-p247/gems/railties-3.2.13/lib/rails/commands.rb:39:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'
```