Adjust rust-version used in CI

Author: 197g

.github/workflows/rust.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: ["1.36.0", stable, beta, nightly]
+        rust: ["1.56.0", stable, beta, nightly]
         command: [build, test]
     steps:
     - uses: actions/checkout@v2
@@ -18,7 +18,7 @@ jobs:
       run: >
         cargo build --verbose
     - name: test
-      if: ${{ matrix.rust != '1.36.0' }}
+      if: ${{ matrix.rust != '1.56.0' }}
       run: >
         cargo test --tests --benches
       # TODO: add criterion benchmarks?