Don't fetch cache inside the web request. If API is slow it leads to …

…timeouts. Background job should do the work to prevent website users from experiencing slow responses.

app/services/exchange_rate_service.rb

@@ -29,7 +29,7 @@ def fetch_external_data
 
   def external_data
     cache = get_cache
-    return cache if cache_valid?(cache)
+    return cache if cache.present?
     fetch_external_data
   end