Using Time.parse to ensure date format is valid

Rakefile

@@ -45,7 +45,7 @@ task :post do
   abort("rake aborted: '#{CONFIG['posts']}' directory not found.") unless FileTest.directory?(CONFIG['posts'])
   title = ENV["title"] || "new-post"
   slug = title.downcase.strip.gsub(' ', '-').gsub(/[^\w-]/, '')
-  date = ENV['date'] || Time.now.strftime('%Y-%m-%d')
+  date = (Time.parse(ENV['date']) || Time.now).strftime('%Y-%m-%d')
   filename = File.join(CONFIG['posts'], "#{date}-#{slug}.#{CONFIG['post_ext']}")
   if File.exist?(filename)
     abort("rake aborted!") if ask("#{filename} already exists. Do you want to overwrite?", ['y', 'n']) == 'n'