switch from failure to anyhow

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

src/backup/fixed_index.rs

@@ -1,4 +1,4 @@
-use failure::*;
+use anyhow::{bail, format_err, Error};
 use std::convert::TryInto;
 use std::io::{Seek, SeekFrom};