Explicitly sort event sessions on upcoming event cards

Even though `event.event_sessions` has an `order` clause,
for some reason it wasn't being used in the context of
rendering the event list. This would cause the event
sessions to be sorted somewhat haphazardly (the sorting
could differ depending on who you were logged in as).

Fixes railsbridge#359

app/views/events/_upcoming_event.html.erb

@@ -7,7 +7,7 @@
     <%= external_links(event) %>
   </div>
   <div class='event-times'>
-    <% event.event_sessions.each_with_index do |session, index| %>
+    <% event.event_sessions.sort_by(&:starts_at).each_with_index do |session, index| %>
       <i class='fa fa-calendar'></i><%= formatted_session_fancy_date(session) %><% if index < event.event_sessions.length - 1 %><br /><% end %>
       <% if event.has_multiple_locations? %>
         <div class='event-session-location'>

spec/features/events/event_listing_request_spec.rb

@@ -36,6 +36,33 @@
     expect(page).to have_content("January 31, #{next_year}")
   end
 
+  describe 'when an upcoming event has many sessions' do
+    it "shows sessions in date order" do
+      event = create(:event,
+                     location_id: nil,
+                     title: 'mytitle2',
+                     time_zone: 'Pacific Time (US & Canada)')
+      create(:event_session, event: event)
+
+      session1, session2 = event.event_sessions.to_a
+      session1.update_attributes(
+        name: 'SecondSession',
+        starts_at: 10.days.from_now,
+        ends_at: 11.days.from_now
+      )
+      session2.update_attributes(
+        name: 'FirstSession',
+        starts_at: 5.days.from_now,
+        ends_at: 6.days.from_now
+      )
+
+      visit events_path
+      within '.event-times' do
+        expect(page).to have_content(/FirstSession.*SecondSession/)
+      end
+    end
+  end
+
   describe "the past events table", js: true do
     before do
       event = create(:event, title: 'InternalPastBridge', time_zone: 'Alaska')