appveyor: use rustc nightly instead of master

Author: matthiaskrgr

appveyor.yml

@@ -20,11 +20,12 @@ install:
     - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
     - git ls-remote https://github.com/rust-lang/rust.git master | awk '{print $1}' >rustc-hash.txt
     - set /p RUSTC_HASH=<rustc-hash.txt
-    - del rust-toolchain
-    - cargo install rustup-toolchain-install-master || echo "rustup-toolchain-install-master already installed"
-    - rustup-toolchain-install-master %RUSTC_HASH% -f -n master
-    - rustup default master
-    - set PATH=%PATH%;C:\Users\appveyor\.rustup\toolchains\master\bin
+# uncomment once https://github.com/rust-lang/rust/issues/55376 is fixed
+#    - del rust-toolchain
+#    - cargo install rustup-toolchain-install-master || echo "rustup-toolchain-install-master already installed"
+#    - rustup-toolchain-install-master %RUSTC_HASH% -f -n master
+#    - rustup default master
+#    - set PATH=%PATH%;C:\Users\appveyor\.rustup\toolchains\master\bin
     - rustc -V
     - cargo -V