Simplify testing arrays exact contents

Instead of testing the contents of each element, we can test the whole
array at once.

spec/models/topic_spec.rb

@@ -37,9 +37,7 @@ describe Topic do
 
       results = community.topics.sort_by_newest
 
-      expect(results.first).to eq(topic3)
-      expect(results.second).to eq(topic2)
-      expect(results.third).to eq(topic1)
+      expect(results).to eq [topic3, topic2, topic1]
     end
 
     it "orders by oldest" do
@@ -68,9 +66,7 @@ describe Topic do
 
       results = community.topics.sort_by_most_commented
 
-      expect(results.first).to eq(topic1)
-      expect(results.second).to eq(topic2)
-      expect(results.third).to eq(topic3)
+      expect(results).to eq [topic1, topic2, topic3]
     end
 
   end