Don't use Cargo-hack for 1.54

Cargo-hack doesn't support it any more.

.github/workflows/main.yml

@@ -15,14 +15,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        build: [stable, 1.54.0, beta, nightly, macos, windows]
+        build: [stable, beta, nightly, macos, windows]
         include:
           - build: stable
             os: ubuntu-latest
             rust: stable
-          - build: 1.54.0
-            os: ubuntu-latest
-            rust: 1.54.0
           - build: beta
             os: ubuntu-latest
             rust: beta
@@ -45,6 +42,21 @@ jobs:
     - name: Run tests
       run: cargo hack test --feature-powerset && cargo hack test --feature-powerset --release
 
+  # Cargo-hack has increase their MSRV above ours, so we can't use it anymore.
+  MSRV:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions-rs/toolchain@v1
+      with:
+        profile: minimal
+        toolchain: 1.46.0
+        override: true
+    - name: Test
+      run: cargo test
+    - name: Test all features
+      run: cargo test --all-features
+
   Rustfmt:
     name: Rustfmt
     runs-on: ubuntu-latest