t/t0002-parser-error.sh: relax test for rack 1.6.0

This overly zealous test was broken by:
rack commit be28c6a2ac152fe4adfbef71f3db9f4200df89e8
("update HTTP status codes to IETF RFC 7231")
remove SSL support

We implemented barely-advertised support for SSL for two reasons:

1) to detect corruption on LANs beyond what TCP offers
2) to support other servers based on unicorn (never happened)

Since this feature is largely not useful for unicorn itself,
there's no reason to penalize unicorn 5.x users with bloat.

In our defense, SSL support appeared in version 4.2.0 :)