Update to Rust 2021 edition

.github/workflows/ci.yml

@@ -33,6 +33,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-latest, ubuntu-latest, windows-latest]
+        toolchain: [stable, 1.56]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2
@@ -40,7 +41,7 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: stable
+          toolchain: ${{ matrix.toolchain }}
           override: true
       - name: Configure cache
         uses: Swatinem/rust-cache@v1

Cargo.toml

@@ -2,8 +2,8 @@
 name = "obws"
 version = "0.8.0"
 authors = ["Dominik Nakamura <dnaka91@gmail.com>"]
-edition = "2018"
-resolver = "2"
+edition = "2021"
+rust-version = "1.56"
 license = "MIT"
 readme = "README.md"
 description = "The obws (obvious) remote control library for OBS."