switch from failure to anyhow

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/backup/chunk_store.rs

@@ -1,4 +1,4 @@
-use failure::*;
+use anyhow::{bail, format_err, Error};
 
 use std::path::{Path, PathBuf};
 use std::io::Write;