patch misplaced period

bot.rb

@@ -64,7 +64,7 @@ bot.message(in: Integer(ENV['SENTENCE_CHANNEL'])) do |event|
     if $sentence.empty?
       next
     end
-    event << "Congratulations, your sentence is: #{$sentence.values.join(" ").}"
+    event << "Congratulations, your sentence is: #{$sentence.values.join(" ")}."
     $sentence.clear
     next
   end