Compile error with log v0.4.20

[chemicstry]

Crate does not compile with log version v0.4.20:

error[E0433]: failed to resolve: could not find `__log_module_path` in `log`
   --> C:\Users\User\.cargo\git\checkouts\rust-fatfs-168a09f1b9eebca0\a3a834e\src\log_macros.rs:54:52
    |
54  |     ($lvl:expr, $($arg:tt)+) => (log!(target: log::__log_module_path!(), $lvl, $($arg)+))
    |                                                    ^^^^^^^^^^^^^^^^^ could not find `__log_module_path` in `log`
    |
   ::: C:\Users\User\.cargo\git\checkouts\rust-fatfs-168a09f1b9eebca0\a3a834e\src\table.rs:496:17
    |
496 |                 warn!("cluster number {} is a special value in FAT to indicate {}; hiding potential FAT chain value {} and instead reporting as a bad sector", cluster, tmp, n);
    |                 --------------------------------------------------------------------------------------------------------------------------------------------------------------- in this macro invocation     
    |
    = note: this error originates in the macro `log` which comes from the expansion of the macro `warn` (in Nightly builds, run with -Z macro-backtrace for more info)

This is because internal log macro depends on unstable API, which was changed in rust-lang/log#570

Temporary workaround for projects depending on this crate: cargo update --precise 0.4.19 log