title: gmap4rails in ActiveAdmin: maps does not appear
body: <p>In try to use gmaps4rails in my ActiveAdmin / Rails app. To do so, I have added the following in my Gemfile:</p>
  
  <pre><code>gem 'gmaps4rails'
  </code></pre>
  
  <p>and ran a "bundle". I updated the 'show' method in app/admin/device.rb file with:</p>
  
  <pre><code>show do 
    attributes_table do
      row :name
    end
  
    # Get device location
    @markers = Location.all.to_gmaps4rails
    div do
      render "map"
    end
  end
  </code></pre>
  
  <p>In the app/views/admin/devices/_map.html.erb I have the following code:</p>
  
  <pre><code>&lt;%= stylesheet_link_tag 'gmaps4rails' %&gt;
  &lt;%= gmaps4rails(@markers) %&gt;
  &lt;%= yield :scripts %&gt;
  </code></pre>
  
  <p>In app/assets/javascripts/application.js:</p>
  
  <pre><code>//= require gmaps4rails/gmaps4rails.googlemaps
  //= require gmaps4rails/gmaps4rails.base
  //= require jquery
  //= require jquery_ujs
  //= require_tree .
  </code></pre>
  
  <p>And in my app/models/location.rb:</p>
  
  <pre><code>class Location &lt; ActiveRecord::Base
    acts_as_gmappable
  
    attr_accessible :latitude, :longitude
  
    def gmaps4rails_address
      "#{self.latitude}, #{self.longitude}" 
    end
  
    def location
      [:latitude, :longitude]
    end
  end
  </code></pre>
  
  <p>When I go on the show page of a device, the map does not shows up (all blank). Is there any configuration I missed ?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I have checked with chrome developer tools and noticed the following error:  </p>
  
  <pre><code>Uncaught SyntaxError: Unexpected token ;
  </code></pre>
  
  <p>that make reference to the line:  </p>
  
  <pre><code>Gmaps.map.markers = ;
  </code></pre>