Update URL for pyftpdlib.

This project was hosted on Google Code, but has moved to github.

BUG=chromium:476190

Review URL: https://codereview.chromium.org/1392213003

Cr-Original-Commit-Position: refs/heads/master@{#353064}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 07d34009edc578b4b103da33606b60945cfcaae2