How to change {1=>2015, 2=>12, 3=>1} format to 2015/12, ruby on rails

First, sorry for my bad english. I'm new to Ruby on rails. I used sunspot gem.

Using facet feature, when I got search result it appears like this {1=>2015, 2=>12, 3=>1} (2) {1=>2015, 2=>11, 3=>1} (1) {1=>2016, 2=>7, 3=>1} (1)

I want it to appear like this 2015/12 (2) 2015/11 (1) 2016/7 (1)

Below is the full method code: index.html.erb

<div id="facets">
  <h3>Published</h3>
  <ul>
    <% for row in @search.facet(:month).rows %>
      <li>
        <% if params[:month].blank? %>
          <%= link_to row.value, :month => row.value %> (<%= row.count %>)
        <% else %>
          <strong><%= row.value %></strong> (<%= link_to "remove", :month => nil %>)
        <% end %>
      </li>
    <% end %>
  </ul>
</div>

trip.rb

searchable do
    text :destination
    string :month

  end

trips_controller.rb

def index
    
    @search = Trip.search do
      
      fulltext params[:search]
     with(:month).greater_than_or_equal_to(Time.zone.now)
      facet(:month)
      with(:month, params[:month]) if params[:month].present?
    end
    @trips = @search.results
    #trips = Trip.where(@filters)
    #@languages = Trip.pluck(:language).uniq
    
    #@interests = Trip.pluck(:interests).uniq
    #@destinations = Trip.pluck(:destination).uniq
  end