Auto merge of #5522 - DarkDrek:user_agent_option, r=alexcrichton
authorbors <bors@rust-lang.org>
Fri, 11 May 2018 23:38:48 +0000 (23:38 +0000)
committerbors <bors@rust-lang.org>
Fri, 11 May 2018 23:38:48 +0000 (23:38 +0000)
Add option to set user-agent

Fixes #5494


Trivial merge