Bugfix: Clean up remaining reference to 3.1.419 (#1446)

* clean up remaining reference to 3.1.419, replacing with newest 3.1 sdk version

* Revert "clean up remaining reference to 3.1.419, replacing with newest 3.1 sdk version"

This reverts commit 2396a29c9c.

* Remove remaining reference to 3.1.419 and replace with a constant

tests/Oryx.BuildImage.Tests/DotNetCore/DotNetCoreSampleAppsTest.cs

@@ -822,7 +822,9 @@ namespace Microsoft.Oryx.BuildImage.Tests
                 () =>
                 {
                     Assert.True(result.IsSuccess);
-                    Assert.Contains(string.Format(SdkVersionMessageFormat, "3.1.419"), result.StdOut);
+                    Assert.Contains(
+                        string.Format(SdkVersionMessageFormat, DotNetCoreSdkVersions.DotNetCore31SdkVersion),
+                        result.StdOut);
                 },
                 result.GetDebugInfo());
         }