use URI::open

app/models/reading.rb

@@ -81,7 +81,7 @@ class Reading < ActiveRecord::Base
       
       url = "https://mijn.easyenergy.com/nl/api/tariff/getapxtariffs?startTimestamp=%s&endTimestamp=%s&grouping=" % [date.strftime("%F %T"),date.advance(:hours => 24).strftime("%F %T")]
       #p urlvandaag
-      json = JSON.load(open(url))
+      json = JSON.load(URI::open(url))
       # advancing with 1 hrs (to offset for something?)
       json.map{|t| [DateTime.parse(t["Timestamp"]).strftime("%F-%H"), [t["TariffUsage"], t["TariffReturn"]]]}.to_h      
     end