Update bitflags minimum version to 1.0.4

[boomshroom]

Currently, this crate requests a version compatible with 1.0.1, but uses the bitflags macro in 2018 style which wasn't supported until bitflags 1.0.4. While running cargo update or starting a new project would bypass the issue, older projects updating their dependencies will see build errors from this crate being unable to find __bitflags. Specifically, I got 41 errors between cannot find macro `__bitflags!` in this scope and various undefined structures defined within bitflags.

Essentially, x86_64 already depends on 1.0.4, but claims to be able to work with 1.0.1 when it really can't.

[phil-opp]

Good catch, thanks a lot for the report!

I pushed a fix in e0d776e and also published a new version to crates.io (0.5.4).