There is a deprecation of both `=~` operator and `%` operator. In 0.13 sigil will be `~r/\Ahttps?:\/\//`. So I want HTTPoison to run without issues on current master and 0.13. One way to achieve it is to remove sigils at all. Another way would be checking what sigil syntax is available by `try Code.eval_string(...)` in compile-time. But I think using binary matching is a better replacement.