Travis CI caching for tests is timing out

[Nemo157]

See for example https://travis-ci.org/rustasync/tide/jobs/534672877#L942-L944

Taking more than 3 minutes probably makes the cache worthless. It's likely that it has accumulated old versions of dependencies that should not be there anymore, I think there are some tools that can cleanup the target directory based on what is actually used in the recent builds so that the cache doesn't keep storing unused data.

[Nemo157]

Tool to investigate using: https://lib.rs/crates/cargo-sweep