Fixed Warning When Using with RSpec

    /.gems/ruby/2.0.0/gems/wunderground-1.1.0/lib/wunderground.rb:45: warning: respond_to? is defined here
    /.gems/ruby/2.0.0/gems/rspec-mocks-2.14.4/lib/rspec/mocks/extensions/marshal.rb:7: warning: Wunderground#respond_to?(:_dump) is old fashion which takes only one parameter