Send initial state in a <script type="application/json"> tag (#1806)

app/views/home/index.html.haml

@@ -1,7 +1,5 @@
 - content_for :header_tags do
-  :javascript
-    window.STREAMING_API_BASE_URL = '#{Rails.configuration.x.streaming_api_base_url}';
-    window.INITIAL_STATE = #{json_escape(render(file: 'home/initial_state', formats: :json))}
+  %script#initial-state{:type => 'application/json'}!= json_escape(render(file: 'home/initial_state', formats: :json))
 
   = javascript_include_tag 'application', integrity: true
 

app/views/home/initial_state.json.rabl

@@ -2,6 +2,7 @@ object false
 
 node(:meta) do
   {
+    streaming_api_base_url: @streaming_api_base_url,
     access_token: @token,
     locale: I18n.locale,
     me: current_account.id,