Disable rustfmt running on AppVeyor for now

rustfmt doesn't seem to execute correctly right now, causing some
backlog of PRs. It's not critical that it runs on Windows, so I've
disabled it for now.

Author: phansch

appveyor.yml

@@ -22,7 +22,7 @@ install:
     - del rust-toolchain
     - cargo install rustup-toolchain-install-master --debug || echo "rustup-toolchain-install-master already installed"
     - rustup-toolchain-install-master %RUSTC_HASH% -f -n master
-    - rustup component add rustfmt --toolchain nightly & exit 0 # Format test handles missing rustfmt
+    # - 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
     - rustc -V