rustup: Download failure of nightly on ARM

Nightly toolchain download fails on ARM while that may not be a problem of rustup itself but Rust’s.

> rustup install nightly-2018-03-26
info: syncing channel updates for 'nightly-2018-03-26-armv7-unknown-linux-gnueabihf'
info: latest update on 2018-03-26, rust version 1.26.0-nightly (482a913fb 2018-03-25)
info: downloading component 'rustc'
 49.7 MiB /  49.7 MiB (100 %)  11.8 MiB/s ETA:   0 s
info: downloading component 'rust-std'
 48.5 MiB /  48.5 MiB (100 %)  12.4 MiB/s ETA:   0 s
info: downloading component 'cargo'
info: downloading component 'rust-docs'
info: installing component 'rustc'
info: installing component 'rust-std'
info: installing component 'cargo'
info: installing component 'rust-docs'

  nightly-2018-03-26-armv7-unknown-linux-gnueabihf installed - rustc 1.26.0-nightly (482a913fb 2018-03-25)

> rustup install nightly-2018-03-27
info: syncing channel updates for 'nightly-2018-03-27-armv7-unknown-linux-gnueabihf'
info: latest update on 2018-03-27, rust version 1.26.0-nightly (188e693b3 2018-03-26)
error: component 'rust-docs' for 'armv7-unknown-linux-gnueabihf' is unavailable for download

> rustup install nightly
info: syncing channel updates for 'nightly-armv7-unknown-linux-gnueabihf'
info: latest update on 2018-04-01, rust version 1.26.0-nightly (517f24025 2018-03-31)
error: component 'rust-docs' for 'armv7-unknown-linux-gnueabihf' is unavailable for download

Meta

rustup

> rustup --version
rustup 1.11.0 (e751ff9f8 2018-02-13)

OS

In crouton environment on Chrome OS,

> cat /etc/os-release
NAME="Ubuntu"
VERSION="16.04.4 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.4 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial

> uname -a
Linux localhost 3.14.0 #1 SMP PREEMPT Wed Mar 14 21:13:13 PDT 2018 armv7l GNU/Linux