Use round instead of floor to calculate number of days

If the time span covered the date when the clocks went forward
then the number of days was off by one.

app/helpers/date_time_helper.rb

@@ -29,7 +29,7 @@ def waiting_for_in_words(date, now = Time.current)
     return unless date.present?
 
     scope = :"petitions.waiting_for_in_words"
-    days  = ((now.end_of_day - date.end_of_day) / 86400.0).floor
+    days  = ((now.end_of_day - date.end_of_day) / 86400.0).round
     key   = WAITING_FOR_KEYS[days]
 
     t(key, scope: scope, formatted_count: number_with_delimiter(days))

spec/helpers/date_time_helper_spec.rb

@@ -74,6 +74,32 @@
       end
     end
 
+    context "when the time span crosses the spring DST boundary" do
+      let(:now) { Time.utc(2016, 4, 11, 11, 0, 0).in_time_zone }
+      let(:date) { 30.days.ago(now) }
+
+      around do |example|
+        travel_to(now) { example.run }
+      end
+
+      it "returns 'Waiting for 30 days'" do
+        expect(helper.waiting_for_in_words(date)).to eq("Waiting for 30 days")
+      end
+    end
+
+    context "when the time span crosses the autumn DST boundary" do
+      let(:now) { Time.utc(2016, 11, 11, 12, 0, 0).in_time_zone }
+      let(:date) { 30.days.ago(now) }
+
+      around do |example|
+        travel_to(now) { example.run }
+      end
+
+      it "returns 'Waiting for 30 days'" do
+        expect(helper.waiting_for_in_words(date)).to eq("Waiting for 30 days")
+      end
+    end
+
     context "when the response threshold was reached 3 years ago" do
       let(:date) { 1095.days.ago(now) }