update minimum walkdir version to 2.2.2 (#432)

notify/Cargo.toml

@@ -23,7 +23,7 @@ crossbeam-channel = { version = "0.5.0", optional = true }
 filetime = "0.2.6"
 libc = "0.2.4"
 serde = { version = "1.0.89", features = ["derive"], optional = true }
-walkdir = "2.0.1"
+walkdir = "2.2.2"
 
 [target.'cfg(target_os="linux")'.dependencies]
 inotify = { version = "0.9", default-features = false }