Auto merge of #5901 - dwijnand:1.28-win, r=alexcrichton

Align AppVeyor to use 1.28 for minimal versions

.. like Travis CI's setup.

Author: bors

appveyor.yml

@@ -13,7 +13,7 @@ install:
   - appveyor-retry appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe
   - rustup-init.exe -y --default-host x86_64-pc-windows-msvc --default-toolchain nightly
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
-  - if defined MINIMAL_VERSIONS rustup toolchain install stable
+  - if defined MINIMAL_VERSIONS rustup toolchain install 1.28.0
   - rustup target add %OTHER_TARGET%
   - rustc -V
   - cargo -V
@@ -27,5 +27,5 @@ test_script:
   # we don't have ci time to run the full `cargo test` with `minimal-versions` like
   # - if defined MINIMAL_VERSIONS cargo +nightly generate-lockfile -Z minimal-versions && cargo +stable test
   # so we just run `cargo check --tests` like
-  - if defined MINIMAL_VERSIONS cargo +nightly generate-lockfile -Z minimal-versions && cargo +stable check --tests
+  - if defined MINIMAL_VERSIONS cargo +nightly generate-lockfile -Z minimal-versions && cargo check --tests
   - if NOT defined MINIMAL_VERSIONS cargo test