multirust fails on Raspbian

multirust output:

```
pi:~ $ curl -sf https://raw.githubusercontent.com/brson/multirust/master/blastoff.sh | sh

Welcome to Rust.

This script will download, build, and install multirust as root, then
configure multirust with the most common options. It may prompt for
your password for installation via 'sudo'.

You may run /usr/local/lib/rustlib/uninstall.sh to uninstall multirust.

Ready? (y/N) y

blastoff: working in temporary directory /tmp/tmp.7siNfyedrV
blastoff: cloning multirust git repo
Cloning into 'multirust'...
remote: Counting objects: 19, done.
remote: Compressing objects: 100% (17/17), done.
remote: Total 19 (delta 1), reused 8 (delta 1), pack-reused 0
Unpacking objects: 100% (19/19), done.
Checking connectivity... done.
blastoff: building
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = "en_US.UTF-8",
LANG = "en_GB.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_GB.UTF-8").
Submodule 'src/rust-installer' (https://github.com/rust-lang/rust-installer) registered for path 'src/rust-installer'
Submodule 'src/rustup' (https://github.com/rust-lang/rustup) registered for path 'src/rustup'
Submodule 'test/multirust-v1' (https://github.com/brson/multirust) registered for path 'test/multirust-v1'
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = "en_US.UTF-8",
LANG = "en_GB.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_GB.UTF-8").
Cloning into 'src/rust-installer'...
remote: Counting objects: 354, done.
remote: Total 354 (delta 0), reused 0 (delta 0), pack-reused 354
Receiving objects: 100% (354/354), 111.83 KiB | 0 bytes/s, done.
Resolving deltas: 100% (215/215), done.
Checking connectivity... done.
Submodule path 'src/rust-installer': checked out 'c37d3747da75c280237dc2d6b925078e69555499'
Cloning into 'src/rustup'...
remote: Counting objects: 358, done.
remote: Total 358 (delta 0), reused 0 (delta 0), pack-reused 358
Receiving objects: 100% (358/358), 167.55 KiB | 0 bytes/s, done.
Resolving deltas: 100% (226/226), done.
Checking connectivity... done.
Submodule path 'src/rustup': checked out 'cb03553d51fb3c72b130c91c25d2aed29d217a24'
Cloning into 'test/multirust-v1'...
remote: Counting objects: 1076, done.
remote: Total 1076 (delta 0), reused 0 (delta 0), pack-reused 1076
Receiving objects: 100% (1076/1076), 305.08 KiB | 0 bytes/s, done.
Resolving deltas: 100% (615/615), done.
Checking connectivity... done.
Submodule path 'test/multirust-v1': checked out '2eaf9067314307320d27be510e1ac3949a21eee9'
blastoff: installing
install: uninstalling component 'multirust'
install: creating uninstall script at /usr/local/lib/rustlib/uninstall.sh
install: installing component 'multirust'

Get ready for Maximum Rust.

blastoff: installing stable toolchain
multirust: installing toolchain 'stable'
rustup: gpg available. signatures will be verified
rustup: downloading manifest for 'stable'
rustup: couldn't find remote installer for 'arm-unknown-linux-gnueabihf' in manifest
blastoff: failed to install stable toolchain. if this appears to be a network problem retry with `multirust default stable`
```