Fixes 4715 - Timezone for Iceland missing from dropdown.

app/models/calendar.rb

@@ -115,7 +115,7 @@ returns
 
   def self.timezones
     list = {}
-    TZInfo::Timezone.all_country_zone_identifiers.each do |timezone|
+    TZInfo::Timezone.all_identifiers.each do |timezone|
       t = ActiveSupport::TimeZone.find_tzinfo(timezone)
       diff = t.current_period.utc_total_offset / 60 / 60
       list[ timezone ] = diff

spec/models/calendar_spec.rb

@@ -455,4 +455,10 @@ RSpec.describe Calendar, type: :model do
       end
     end
   end
+
+  describe '.timezones' do
+    it 'includes known zones' do
+      expect(described_class.timezones.keys).to include('GMT', 'Europe/Berlin', 'Atlantic/Reykjavik')
+    end
+  end
 end