Doesn't work with truncated hashes #40
Description
$ rustup-toolchain-install-master c963187
detecting the channel of the `c963187` toolchain...
error: toolchain `c963187` doesn't exist in any channel
$ rustup-toolchain-install-master c963187c6f959417cbb13a33e9eaea4607696fc4 1 ✘
detecting the channel of the `c963187c6f959417cbb13a33e9eaea4607696fc4` toolchain...
downloading <https://ci-artifacts.rust-lang.org/rustc-builds/c963187c6f959417cbb13a33e9eaea4607696fc4/rustc-nightly-x86_64-unknown-linux-gnu.tar.xz>...
50.60 MB / 50.60 MB [========================================================================================================================================================================] 100.00 % 11.49 MB/s
downloading <https://ci-artifacts.rust-lang.org/rustc-builds/c963187c6f959417cbb13a33e9eaea4607696fc4/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz>...
24.49 MB / 24.49 MB [========================================================================================================================================================================] 100.00 % 10.94 MB/s
toolchain `c963187c6f959417cbb13a33e9eaea4607696fc4` is successfully installed!
I'm not sure if it's possible to find the matching build for a truncated hash, but an error message might be useful here.