Docker builds failing 'cfg(doctest)' from xlm-rs

[btrepp]

Steps to reproduce

cargo func new-app myapp
docker build -t domain/app .

Expected behavior

Docker build would create a dockerfile

Actual behavior

Rust in the container fails to compile.

error[E0658]: `cfg(doctest)` is experimental and subject to change
#15 54.21  --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/xml-rs-0.8.2/src/lib.rs:9:7
#15 54.21   |
#15 54.21 9 | #[cfg(doctest)]
#15 54.21   |       ^^^^^^^
#15 54.21   |
#15 54.21   = note: for more information, see https://github.com/rust-lang/rust/issues/62210

I suspect maybe the builder image has a older version of rust, and bumping that might resolve the issue?.

Environment information (OS, versions, etc.)

Docker
-Tried on windows and ubuntu in azure devops.

Compiles fine locally (in release on windows) using cargo 1.41.0 (626f0f40e 2019-12-03) and rust version
rustc --version rustc 1.41.1 (f3e1a954d 2020-02-24)

[btrepp]

So I've docker built the builder image, fixed some build issues with it (tweaked some SSL package issues) and that does allow the functions to build, unsure currently whether I need to tweak the runtime.

I've pushed the image to "btrepp/azure-functions-builder" in dockerhub in case anyone needs to use/try it.