Bump CI from Rust 1.40 to 1.46

Bitflags 1.3.0/1.3.1 requires Rust 1.46 to compile, and that is dragged
in via the openssl package.

Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                rust: [1.40.0, stable, nightly]
+                rust: [1.46.0, stable, nightly]
         steps:
         - uses: actions/checkout@v2
         - uses: dtolnay/rust-toolchain@master