Improve URL validation to check for a valid host.

Parsing a URL with `URI` is not sufficient as the following cases
are considered valid:

URI.parse("http://https://google.com")
=> #<URI::HTTP http://https//google.com>

lib/validators/url_validator.rb

@@ -1,9 +1,15 @@
 class UrlValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     if value.present?
-      uri = URI.parse(value) rescue nil
+      valid =
+        begin
+          uri = URI.parse(value)
+          uri.is_a?(URI::HTTP) && !uri.host.nil? && uri.host.include?(".")
+        rescue
+          nil
+        end
 
-      unless uri
+      unless valid
         record.errors[attribute] << (options[:message] || I18n.t('errors.messages.invalid'))
       end
     end