doc.rs broken for recent versions

[brayniac]

docs.rs builds fail for the momento crate with version 0.5.3 being the last successful doc build. I haven't looked too closely, but the build logs are available docs.rs/momento - relevant error appears to be:

[INFO] [stderr] thread 'main' panicked at 'Failed to compile protos Os { code: 30, kind: ReadOnlyFilesystem, message: "Read-only file system" }', /opt/rustwide/cargo-home/registry/src/github.com-1ecc6299db9ec823/momento-protos-0.18.1/build.rs:12:29

I think this is a pretty significant barrier in terms of usage. Most people looking to use a rust crate will reference docs.rs for the relevant library documentation. If this documentation is stale (as is the case currently) it creates friction while trying to work with a crate.

It's possible that the only fix needs to be applied to the momento-protos crate, but flagging here as I anticipate most users would use the momento crate and not the protos crate.