Change MSRV in github workflows

Author: hoxxep

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        rust: ["1.66", stable, beta, nightly]
+        rust: ["1.60", stable, beta, nightly]
         os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
     - uses: actions/checkout@master