Use core HTTP::Tiny instead of Furl

Given that under Travis this module is installed for every test run, reducing it's dependencies can have a measurable effect on test run time.

HTTP::Tiny, unlike Furl is in core, by swapping the two modules we no longer need to install Furl or it's dependencies of Class::Accessor::Lite & HTTP::Parser::XS.

IO::Socket::SSL >= 1.42 & Net::SSLeay >= 1.49 are required for SSL support in HTTP::Tiny.

HTTP::Tiny by default won't check certificates, by installing Mozilla::CA and setting verify_SSL at construction time we get the same level of experience as Furl, with Coverall's certificate being checked against the Mozilla database.

Next step, it's annoying that Devel::Cover installs CGI, especially given we're not even using the HTML reports :-P