Test minimal versions in CI (#223)

.github/workflows/rust.yml

@@ -12,6 +12,13 @@ jobs:
         rust: ["1.61.0", stable, beta, nightly]
     steps:
     - uses: actions/checkout@v2
+
+    - uses: dtolnay/rust-toolchain@nightly
+      if: ${{ matrix.rust == '1.61.0' }}
+    - name: Generate Cargo.lock with minimal-version dependencies
+      if: ${{ matrix.rust == '1.61.0' }}
+      run: cargo -Zminimal-versions generate-lockfile
+
     - uses: dtolnay/rust-toolchain@v1
       with:
         toolchain: ${{ matrix.rust }}
@@ -19,9 +26,6 @@ jobs:
       uses: Swatinem/rust-cache@v2
       with:
         cache-on-failure: true
-    - name: Install MSRV Cargo.lock
-      if: ${{ matrix.rust == '1.61.0' }}
-      run: mv Cargo.lock.msrv Cargo.lock
     - name: build
       run: cargo build -v
     - name: test
@@ -46,16 +50,3 @@ jobs:
       with:
         components: clippy
     - run: cargo clippy --all-features # TODO: enable "-- -D warnings" once all outstanding clippy lints are fixed
-
-  verify_msrv:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install or use cached `cargo-msrv`
-        uses: baptiste0928/cargo-install@v1
-        with:
-          crate: cargo-msrv
-      - name: Install MSRV Cargo.lock
-        run: mv Cargo.lock.msrv Cargo.lock
-      - name: Verify Minimum Rust Version
-        run: cargo-msrv verify