Merge pull request #58 from image-rs/polish

Update dev-dependencies used in the project

Author: 197g

.github/workflows/rust.yml

@@ -22,7 +22,7 @@ jobs:
     - name: test
       run: >
         cargo test --tests --benches --no-default-features --features "$FEATURES" --release
-      if: ${{ matrix.rust != '1.34.2' }}
+      if: ${{ matrix.rust != '1.56.0' }}
       env:
         FEATURES: ${{ matrix.features }}
   build_msrv:
@@ -32,7 +32,7 @@ jobs:
         features: ["", "std"]
     steps:
     - uses: actions/checkout@v2
-    - run: rustup default "1.34.2"
+    - run: rustup default "1.56.0"
     - name: build
       run: cargo build --verbose --no-default-features --features "$FEATURES"
       env: