Revise test workaround comments

Author: bording

LibGit2Sharp.Tests/RepositoryFixture.cs

@@ -167,8 +167,8 @@ private static void CheckGitConfigFile(string dir)
 
         private static void AssertIsHidden(string repoPath)
         {
-            //Work around .NET Core handling calls to File.GetAttributes with paths with a trailing slash differently
-            //without removing the trailing slash, the Hidden attribute is not included.
+            //Workaround for .NET Core 1.x never considering a directory hidden if the path has a trailing slash
+            //https://github.com/dotnet/corefx/issues/18520
             repoPath = repoPath.TrimEnd('/');
 
             FileAttributes attribs = File.GetAttributes(repoPath);

LibGit2Sharp.Tests/TestHelpers/BaseFixture.cs

@@ -389,7 +389,8 @@ protected static string Touch(string parent, string file, string content = null,
 
             File.WriteAllText(filePath, content ?? string.Empty, encoding ?? Encoding.ASCII);
 
-            //Work around .NET Core 1.x behavior where all newly created files have execute permissions set.
+            //Workaround for .NET Core 1.x behavior where all newly created files have execute permissions set.
+            //https://github.com/dotnet/corefx/issues/13342
             if (Constants.IsRunningOnUnix && newFile)
             {
                 RemoveExecutePermissions(filePath, newFile);
@@ -417,6 +418,7 @@ protected static string Touch(string parent, string file, Stream stream)
             }
 
             //Work around .NET Core 1.x behavior where all newly created files have execute permissions set.
+            //https://github.com/dotnet/corefx/issues/13342
             if (Constants.IsRunningOnUnix && newFile)
             {
                 RemoveExecutePermissions(filePath, newFile);