drop msys-gnu appveyor conf and skip appveyor cache restore

appveyor.yml

@@ -4,35 +4,21 @@
 environment:
   global:
     RUST_VERSION: stable
-
+    APPVEYOR_CACHE_SKIP_RESTORE: true
     CRATE_NAME: skeptic
 
   matrix:
-    # MinGW
-    - TARGET: i686-pc-windows-gnu
-    - TARGET: x86_64-pc-windows-gnu
-
     # MSVC
     - TARGET: i686-pc-windows-msvc
     - TARGET: x86_64-pc-windows-msvc
 
     # Testing other channels
-    - TARGET: x86_64-pc-windows-gnu
-      RUST_VERSION: beta
     - TARGET: x86_64-pc-windows-msvc
       RUST_VERSION: beta
-    - TARGET: x86_64-pc-windows-gnu
-      RUST_VERSION: nightly
     - TARGET: x86_64-pc-windows-msvc
       RUST_VERSION: nightly
 
 install:
-  - ps: >-
-      If ($Env:TARGET -eq 'x86_64-pc-windows-gnu') {
-        $Env:PATH += ';C:\msys64\mingw64\bin'
-      } ElseIf ($Env:TARGET -eq 'i686-pc-windows-gnu') {
-        $Env:PATH += ';C:\msys64\mingw32\bin'
-      }
   - curl -sSf -o rustup-init.exe https://win.rustup.rs/
   - rustup-init.exe -y --default-host %TARGET% --default-toolchain %RUST_VERSION%
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
@@ -54,13 +40,6 @@ test_script:
 
 cache:
   - C:\Users\appveyor\.cargo\registry
-  - target
-
-branches:
-  only:
-    # Release tags
-    - /^v\d+\.\d+\.\d+.*$/
-    - master
 
 notifications:
   - provider: Email