Make it compatible with Node 10.0 - 10.7

[mildsunrise]

Turns out it was easy :)

However, I had to patch binding.gyp as indicated here, otherwise the code used system OpenSSL headers instead of Node.JS version of OpenSSL.

[mildsunrise]

Aaaand it turns out this is also happening in Travis. I'll take a look.

[mildsunrise]

It's a bug in node-gyp that was fixed in node-gyp 3.7.0.
Node.JS 10.0 only has node-gyp 3.6.2.

[mildsunrise]

I've ended up backporting the fix (it's two includes)

[kolontsov]

Great work! it compiles and runs simple tests.

However I have concerns about &(*ssl_) (which makes code compatible with both SSL* and std::unique_ptr<SSL>), because operator* has undefined behaviour if get() returns nullptr, or if we're dereferencing NULL SSL* pointer. In our case it seems to work with null pointer because we use &*, but.. can we please switch to #ifdef or something like this, to use return ssl_ for <=10.7 and return ssl_.get() in other cases?

[mildsunrise]

Done!