Merge pull request #3149 from rust-lang/renovate/num_cpus-1.x

Update Rust crate num_cpus to 1.15

Author: rbtcollins

Cargo.lock

@@ -38,7 +38,7 @@ git-testament = "0.2"
 home = "0.5.4"
 lazy_static = "1"
 libc = "0.2"
-num_cpus = "1.13"
+num_cpus = "1.15"
 opener = "0.5.0"
 # Used by `curl` or `reqwest` backend although it isn't imported
 # by our rustup.