Switch Apache logo URL to HTTPS

Hi,

Reading Kafka webpage/documentation through HTTPS (e.g.
https://kafka.apache.org/documentation.html) I spotted that it generates
warning (in Firefox and Chromium) about a reference to unencrypted
resources. In fact the Apache logo is always load using HTTP -
http://www.apache.org/images/feather-small.png

As that image is also available via HTTPS I think it would painless to
switch "src" in "img" tag in
https://svn.apache.org/repos/asf/kafka/site/includes/footer.html to
HTTPS or use double slash syntax which was defined in 15+ years old RFC
1808 and should be supported by recent browsers -
http://stackoverflow.com/a/9632363/313516

Marcin