reused value of Time.now in a method

`Time.now` was being used to fetch the current time, twice in the
same line. This commit stores the time value in a variable and
reuses it instead of generating/fetching it for the second time.

Additionally, a guard clause in the same method is substituted by
an `if/else/end` block for clarity.

lib/age_words.rb

@@ -1,8 +1,12 @@
 module AgeWords
 
   def self.age_words(secs)
-    return "—" if secs.blank?
-    return FreedomPatches::Rails4.distance_of_time_in_words(Time.now, Time.now + secs)
+    if secs.blank?
+      "—"
+    else
+      now = Time.now
+      FreedomPatches::Rails4.distance_of_time_in_words(now, now + secs)
+    end
   end
 
 end