deprecated associated function in build

[mikemadden42]

$ rustc --version
rustc 1.52.1 (9bc8c42bb 2021-05-09)

$ sw_vers
ProductName:	macOS
ProductVersion:	11.3.1
BuildVersion:	20E241

I see this warning from cargo build --release:

   Compiling reqwest v0.11.3
warning: use of deprecated associated function `failure::Fail::causes`: please use the 'iter_chain()' method instead
  --> src/util.rs:59:10
   |
59 |         .causes()
   |          ^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: 1 warning emitted

[timvisee]

Thanks for the report. This shows up on all systems and configurations.

This is related to error handling. In order to properly fix this I'd like to upgrade to using the thiserror and anyhow crates (like I've done with prs).

I currently have limited time available, sadly. Fixing this as suggested requires some time for plumbing work. As it's a low priority thing I'll leave it open for a later moment to fix.

This has also been reported here: https://gitlab.com/timvisee/ffsend/-/issues/110