Incorrect feature name in `linux_session`

[rydrman]

First off, I am really enjoying this library, so thank you. I've noticed an issue using asyncio on linux, where the code is conditional on a feature that doesn't exist (notice the _ instead of -)

fuse-backend-rs/src/transport/fusedev/linux_session.rs

Line 405 in f18d4be

#[cfg(feature = "async_io")]

fuse-backend-rs/src/transport/fusedev/linux_session.rs

Line 408 in f18d4be

#[cfg(feature = "async_io")]

[PlamenHristov]

Hey,

Please see my comment on #188