Support https url scheme (add Faker::Internet.secure_url)

[juyeong]

for issue #459
I just added Faker::Internet.secure_url to create fake https url.
Maybe it would be better if url method support all url components like
Faker::Internet.url(scheme: 'https', domain: 'example.org')
but it is not good to make breaking changes. so I just added new method

[DanDobrick]

@juyeong: why don't you make scheme have default as http?

Faker::Internet.url(host = domain_name, path = "/#{user_name}", scheme = 'http')
Faker::Internet.url(host = domain_name, path = "/#{user_name}", scheme = 'https')

[stympy]

Closed in favor of #747.