title: elasticsearch-rails not a geopoint field error
body: <p>i tried to implement geo distance search with elasticsearch-rails but i am getting not a geopoint field error also triend with string version of latitude and longitude. i am using elasticsearch version 1.0.2</p>
  
  <pre><code>error 
  "error_code": "103",
      "error_message": "[400] {\"error\":\"SearchPhaseExecutionException[Failed to execute phase [query], all shards failed; shardFailures {[IiAHsrYDQW-nDOBQYlVHpg][barter_li_application_development][3]: SearchParseException[[barter_li_application_development][3]: query[title:rty*],from[-1],size[-1]: Parse Failure [Failed to parse source [{\\\"query\\\":{\\\"prefix\\\":{\\\"title\\\":\\\"rty\\\"}},\\\"filter\\\":{\\\"geo_distance\\\":{\\\"distance\\\":50,\\\"lon_lat\\\":{\\\"lon\\\":\\\"12\\\",\\\"lat\\\":\\\"12\\\"}}}}]]]; nested: QueryParsingException[[barter_li_application_development] field [lon_lat] is not a geo_point field]; }{[IiAHsrYDQW-nDOBQYlVHpg][barter_li_application_development][4]: SearchParseException[[barter_li_application_development][4]: query[title:rty*],from[-1],size[-1]: Parse Failure [Failed to parse source [{\\\"query\\\":{\\\"prefix\\\":{\\\"title\\\":\\\"rty\\\"}},\\\"filter\\\":{\\\"geo_distance\\\":{\\\"distance\\\":50,\\\"lon_lat\\\":{\\\"lon\\\":\\\"12\\\",\\\"lat\\\":\\\"12\\\"}}}}]]]; nested: QueryParsingException[[barter_li_application_development] field [lon_lat] is not a geo_point field]; }{[IiAHsrYDQW-nDOBQYlVHpg][barter_li_application_development][1]: SearchParseException[[barter_li_application_development][1]: query[title:rty*],from[-1],size[-1]: Parse Failure [Failed to parse source [{\\\"query\\\":{\\\"prefix\\\":{\\\"title\\\":\\\"rty\\\"}},\\\"filter\\\":{\\\"geo_distance\\\":{\\\"distance\\\":50,\\\"lon_lat\\\":{\\\"lon\\\":\\\"12\\\",\\\"lat\\\":\\\"12\\\"}}}}]]]; nested: QueryParsingException[[barter_li_application_development] field [lon_lat] is not a geo_point field]; }{[IiAHsrYDQW-nDOBQYlVHpg][barter_li_application_development][2]: SearchParseException[[barter_li_application_development][2]: query[title:rty*],from[-1],size[-1]: Parse Failure [Failed to parse source [{\\\"query\\\":{\\\"prefix\\\":{\\\"title\\\":\\\"rty\\\"}},\\\"filter\\\":{\\\"geo_distance\\\":{\\\"distance\\\":50,\\\"lon_lat\\\":{\\\"lon\\\":\\\"12\\\",\\\"lat\\\":\\\"12\\\"}}}}]]]; nested:
  </code></pre>
  
  <p>the code</p>
  
  <pre><code>   module Searchable
        extend ActiveSupport::Concern
  
        included do
          include Elasticsearch::Model
          include Elasticsearch::Model::Callbacks
  
  
          # Customize the index name
          #
          index_name [Rails.application.engine_name, Rails.env].join('_')
  
          # Set up index configuration and mapping
          #
          settings index: { number_of_shards: 1, number_of_replicas: 0 } do
            mapping do
              # indexes :title, type: 'multi_field' do
                indexes :title,     analyzer: 'not_analyzed'
              #   indexes :tokenized, analyzer: 'simple'
              # end
              indexes :lon_lat, type: 'geo_point'
            end
          end
  
  
          # Set up callbacks for updating the index on model changes
          #
          # after_commit lambda { Indexer.perform_async(:index,  self.class.to_s, self.id) }, on: :create
          # after_commit lambda { Indexer.perform_async(:update, self.class.to_s, self.id) }, on: :update
          # after_commit lambda { Indexer.perform_async(:delete, self.class.to_s, self.id) }, on: :destroy
          # after_touch  lambda { Indexer.perform_async(:update, self.class.to_s, self.id) }
  
          # Customize the JSON serialization for Elasticsearch
          #
          def as_indexed_json(options={})
            {
              title: self.title,
              lon_lat: lon_lat
            }
          end
  
        def lon_lat
             [self.location.longitude.to_f, self.location.latitude.to_f]
         end
  
  
        def self.search(query)
          __elasticsearch__.search(
            {
              query: { prefix:  { title: query[:title] } },
              filter: {
                  geo_distance: {
                      distance: query[:radius],
                      lon_lat: {
                        lon: query[:longitude],
                        lat: query[:latitude]
  
                      }
                  }
                }
            }
          )
        end
       end
      end
  </code></pre>