Fix Dutch country code

+31 is the Dutch country code.

See: https://en.wikipedia.org/wiki/Telephone_numbers_in_the_Netherlands

Author: klaaspieter

lib/locales/nl.yml

@@ -83,6 +83,8 @@ nl:
         - "#{first_name} #{last_name} #{last_name}"
 
     phone_number:
+      country_code:
+        - '31'
       formats: ["(####) ######", "##########", "06########", "06 #### ####"]
 
     university:

test/test_nl_locale.rb

@@ -65,6 +65,12 @@ def test_nl_phone_number_methods
     assert_kind_of String, Faker::PhoneNumber.cell_phone
   end
 
+  def test_nl_cell_phone_countrycode
+    mobile = Faker::PhoneNumber.cell_phone_with_country_code.gsub(/\D/, '')
+
+    assert_match(/^(0|31)/, mobile)
+  end
+
   def test_nl_university_methods
     assert_kind_of String, Faker::University.prefix
     assert_kind_of String, Faker::University.name