Fixes CURLINFO_HEADER_SIZE of versions below 7.30

refs: https://sourceforge.net/p/curl/bugs/1204/

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>
show curl version in travis

Signed-off-by: Benoît Burnichon <bburnichon@gmail.com>
Merge pull request #156 from bburnichon/curl_proxy_issue

Curl proxy header issue