Update the rust-installer submodule

This pulls in a commit which uses parallel xz encoding which should
hopefully help shave some time off the dist builders which spend an
inordinate amount of time compressing this data.

Author: alexcrichton

Cargo.lock

@@ -1272,9 +1272,10 @@ name = "installer"
 version = "0.0.0"
 dependencies = [
  "clap 2.32.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "failure 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num_cpus 1.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "tar 0.4.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 2.2.7 (registry+https://github.com/rust-lang/crates.io-index)",