remove windows 2019 from github CI due to old rustc

Author: valpackett

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [windows-2019, windows-latest]
+        os: [windows-latest]
     steps:
     - uses: actions/checkout@v1
     - name: Build