developer-certificate-of-origin: Update LF address

developer-certificate-of-origin: Update LF address

By pulling a fresh copy.  Also, developercertificate.org now support
TLS :)

  $ wget -S -O developer-certificate-of-origin https://developercertificate.org/
  --2017-10-11 11:03:49--  https://developercertificate.org/
  Resolving developercertificate.org... 140.211.169.4
  Connecting to developercertificate.org|140.211.169.4|:443... connected.
  HTTP request sent, awaiting response...
    HTTP/1.1 200 OK
    Server: nginx
    Date: Wed, 11 Oct 2017 18:01:49 GMT
    Content-Type: text/html; charset=UTF-8
    Content-Length: 1732
    Connection: keep-alive
    Vary: Accept-Encoding
    Last-Modified: Thu, 30 Jun 2016 17:31:34 GMT
    ETag: "5c2e43-6c4-536823dd5ef81"
    Strict-Transport-Security: max-age=16070400
    Accept-Ranges: bytes
  Length: 1732 (1.7K) [text/html]
  Saving to: ‘developer-certificate-of-origin’
  ...

After which I stripped out the HTML, leaving just the DCO text.

Signed-off-by: W. Trevor King <wking@tremily.us>