Use latest stable Rust

We don't need to commit to an MSRV yet, and this avoids the problem
where some of our in-flux dependencies bump their MSRV (or don't have
a defined MSRV and make changes to use more recent features) causing
our CI to break.

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.45.2
+          toolchain: stable
           override: true
       - name: Run tests
         uses: actions-rs/cargo@v1
@@ -32,7 +32,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.45.2
+          toolchain: stable
           override: true
       # Build benchmarks to prevent bitrot
       - name: Build benchmarks
@@ -42,7 +42,7 @@ jobs:
           args: --all --benches --all-features
 
   clippy:
-    name: Clippy (1.45.2)
+    name: Clippy (stable)
     timeout-minutes: 30
     runs-on: ubuntu-latest
 
@@ -50,13 +50,13 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: 1.45.2
+          toolchain: stable
           components: clippy
           override: true
       - name: Run clippy
         uses: actions-rs/clippy-check@v1
         with:
-          name: Clippy (1.45.2)
+          name: Clippy (stable)
           token: ${{ secrets.GITHUB_TOKEN }}
           args: --all-features --all-targets -- -D warnings