Use Date class to assist with date math in Project model

Fixes an intermittent failure in ProjectTest#test_age_in_days

app/models/project.rb

@@ -136,7 +136,7 @@ class Project < ActiveRecord::Base
   end
 
   def age_in_days
-    @age_in_days ||= ((Time.now.utc - created_at).to_i / 1.day) + 1
+    @age_in_days ||= (Time.now.to_date - created_at.to_date).to_i + 1
   end
 
   def self.import(filename, params, user)