Replaced .NET SDK versions.

Author: lextm

.github/workflows/dotnetcore.yml

@@ -13,9 +13,8 @@ jobs:
       uses: actions/setup-dotnet@v1
       with:
         dotnet-version: |
-          3.1.x
-          5.0.x
           6.0.x
+          7.0.x
     - name: Build
       shell: bash
       run: |
@@ -37,9 +36,8 @@ jobs:
       uses: actions/setup-dotnet@v1
       with:
         dotnet-version: |
-          3.1.x
-          5.0.x
           6.0.x
+          7.0.x
     - name: Build
       shell: bash
       run: |
@@ -63,9 +61,8 @@ jobs:
       uses: actions/setup-dotnet@v1
       with:
         dotnet-version: |
-          3.1.x
-          5.0.x
           6.0.x
+          7.0.x
     - name: Build
       shell: cmd
       run: build.release.bat