Compat/ruby 2.7.1

[drbig]

Minimal viable :hammer: addressing #10. I'm running ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux] and this minimal set of changes makes stuff seem to work. As I'm vastly more interested in tinkering with a specific use-case of a MITM HTTP Proxy and being time-constrained I'm PRing this solely as "hey, seems to work for me, do what you want with it".

Caveats:

• Haven't even try to run with any other Ruby version; I'm assuming these changes break compat at least with <2.7.x
• "I have no idea what I'm doing", as in: don't know the correct behavior of evil-proxy so can't judge beyond "stuff seems to work for me"

Thanks! I'm gonna go back to my tinkering :)