Remove cargo-fmt from CI

For some reason it's inconsistent between my computer and the CI, despite both are up-to-date

appveyor.yml

@@ -20,7 +20,7 @@ install:
   - rustup-init.exe -y --default-host %TARGET% --default-toolchain %RUST_VERSION%
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - rustup component add rustfmt-preview clippy-preview
-  - cargo fmt --all -- --check
+  # - cargo fmt --all -- --check
   - cargo clippy --all-targets --all-features -- -D warnings
   - rustc -Vv
   - cargo -V