Revert "rustc-dev has been temporarily removed"

This reverts commit 974a05b.

Author: flip1995

CONTRIBUTING.md

@@ -147,7 +147,7 @@ You can use [rustup-toolchain-install-master][rtim] to do that:
 
 ```bash
 cargo install rustup-toolchain-install-master
-rustup-toolchain-install-master --force -n master
+rustup-toolchain-install-master --force -n master -c rustc-dev
 rustup override set master
 cargo test
 ```

appveyor.yml

@@ -25,7 +25,7 @@ install:
     - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
     - del rust-toolchain
     - cargo install -Z install-upgrade rustup-toolchain-install-master
-    - rustup-toolchain-install-master -f -n master
+    - rustup-toolchain-install-master -f -n master -c rustc-dev
     - rustup component add rustfmt --toolchain nightly & exit 0 # Format test handles missing rustfmt
     - rustup default master
     - set PATH=%PATH%;C:\Users\appveyor\.rustup\toolchains\master\bin

setup-toolchain.sh

@@ -9,5 +9,5 @@ if [[ "$CI" == true ]] || ! command -v rustup-toolchain-install-master > /dev/nu
   cargo install -Z install-upgrade rustup-toolchain-install-master --bin rustup-toolchain-install-master
 fi
 
-rustup-toolchain-install-master -f -n master
+rustup-toolchain-install-master -f -n master -c rustc-dev
 rustup override set master