Update dotnetcore.yml

Author: mjebrahimi

.github/workflows/dotnetcore.yml

@@ -3,10 +3,10 @@ name: .NET Core
 on:
   push:
     paths-ignore:
-      - 'readme.md'
+      - 'README.md'
   pull_request:
     paths-ignore:
-      - 'readme.md'
+      - 'README.md'
 
 jobs:
   build:
@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v2.3.4
 
     - name: Build (Release)
       run: dotnet build --configuration Release