lower msrv to 1.43

.github/workflows/rust.yml

@@ -30,4 +30,19 @@ jobs:
       - uses: Swatinem/rust-cache@v1
       - uses: actions-rs/cargo@v1
         with:
-          command: test
+          command: test
+
+  msrv:
+    name: Check MSRV
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: 1.43
+          override: true
+      - uses: Swatinem/rust-cache@v1
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check