Update README.md

Author: maxim-lobanov

README.md

@@ -22,11 +22,8 @@ jobs:
     name: Setup Xamarin and Mono versions
     runs-on: macos-latest
     steps:
-    - name: Checkout
-      uses: actions/checkout@master
-
     - name: setup-xamarin
-      uses: maxim-lobanov/setup-xamarin
+      uses: maxim-lobanov/setup-xamarin@v1.1
       with:
         mono-version: 6.6 # specify version in '<major>.<minor>' format
         xamarin-ios-version: 13 # specify version in '<major>' format