eval'ing fails on non-JSON S2S response body

[oehlschl]

Reported in PX chat, but we're seeing the following error after some S2S calls:

perimeterx/internal/validators/perimeter_x_s2s_validator.rb:87:in `eval': (eval):2: syntax error, unexpected '<'

I'm guessing that the < is the opening of an HTML tag, and that for some reason PX is returning a non-JSON (maybe error) response.

This occurs here:
https://github.com/PerimeterX/perimeterx-ruby-sdk/blob/master/lib/perimeterx/internal/validators/perimeter_x_s2s_validator.rb#L87

IMO the response body shouldn't be parsed until the response code is checked (which currently happens on the line below).