Bump CI rust version

Author: sfackler

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: sfackler/actions/rustup@master
         with:
-          version: 1.37.0
+          version: 1.42.0
       - run: echo "::set-output name=version::$(rustc --version)"
         id: rust-version
       - uses: actions/cache@v1