Request: yank minimal-versions incompliant releases #60

Interestingly, changing between proc-macro-hack 0.5.6 and 0.5.7 only changes the version of proc-macro-hack and doesn't impact the rest of the tree. It seems to be the only difference is whether the default feature set is used.

Honestly, it might make sense to yank so the minimal 0.5 version is 0.5.9 so the people still trying to use minimal-versions don't end up dealing with pre-1.0 syn/quote via proc-macro-hack.

This isn't urgent nor even blocking minimal-versions correctness for any of my crates; I've just decided not to enable ahash's compile-time-random support, which dropped proc-macro-hack out of the dependency tree of the crate where I found this out.