chore: replace ri_cal with icalendar

based upon rubyredrick/ri_cal#22 (comment) i assume phoet intended to replace the quite outdated ri_cal with icalendar a while ago.
so doing it now :)

Gemfile

@@ -22,7 +22,7 @@ gem 'public_suffix'
 gem 'puma'
 gem 'rack-cache'
 gem 'redcarpet'
-gem 'ri_cal', github: 'phoet/ri_cal', branch: 'master'
+gem 'icalendar'
 gem 'simple_form'
 gem 'slim-rails'
 gem 'sprockets', '~> 3.7'

Gemfile.lock

@@ -1,12 +1,3 @@
-GIT
- remote: https://github.com/phoet/ri_cal.git
- revision: 0c607408f931ebbbed1c5e4dd6e4eb22572f268f
- branch: master
- specs:
- ri_cal (0.8.8)
- activesupport (> 2.2)
- tzinfo (> 2.0)
-
 GEM
  remote: http://rubygems.org/
  specs:
@@ -135,6 +126,9 @@ GEM
  hashie (5.0.0)
  i18n (1.14.4)
  concurrent-ruby (~> 1.0)
+ icalendar (2.10.2)
+ ice_cube (~> 0.16)
+ ice_cube (0.17.0)
  image_info (1.2.2)
  addressable (~> 2.0)
  image_size (~> 2.0)
@@ -459,6 +453,7 @@ DEPENDENCIES
  faker
  font-awesome-rails
  geocoder
+ icalendar
  kaminari
  kgio
  letter_opener
@@ -480,7 +475,6 @@ DEPENDENCIES
  rails-controller-testing
  rails_12factor
  redcarpet
- ri_cal!
  rspec-collection_matchers
  rspec-rails
  rubocop

app/helpers/ical_helper.rb

@@ -2,18 +2,18 @@
 
 module IcalHelper
  def icalendar(*events)
- RiCal.Calendar do |cal|
- events.each do |event|
- cal.event do |item|
- item.summary = event.name
- item.description = "#{event.description} #{event_url(event)}"
- item.dtstart = event.date
- item.dtend = event.end_date
- item.url = event_url(event)
- item.location = event.location.name if event.location
- end
+ cal = Icalendar::Calendar.new
+ events.map do |event|
+ cal.event do |item|
+ item.summary = event.name
+ item.description = "#{event.description} #{event_url(event)}"
+ item.dtstart = event.date
+ item.dtend = event.end_date
+ item.url = event_url(event)
+ item.location = event.location.name if event.location
  end
- end.to_s
+ end
+ cal.to_ical
  end
 
  def calendar_link