title: Searchkick boost_by_distance gives undefined method `reverse'
body: <p>What am I missing here? I simply copy paste the example on <a href="https://github.com/ankane/searchkick" rel="nofollow">https://github.com/ankane/searchkick</a> to the console and I get an error.</p>
  
  <p>2.2.2 :001 > User.search "jim", boost_by_distance: {field: :location, origin: {lat: 37, lon: -122}}
  NoMethodError: undefined method `reverse' for {:lat=>37, :lon=>-122}:Hash</p>