single-db mode single file option needs to use same method as full database mode

Author: AlanBarber

src/BitCheck/Application/BitCheckApplication.cs

@@ -275,7 +275,7 @@ private void ProcessSingleFile(string filePath)
             if (_options.SingleDatabase)
             {
                 // In single-db mode, use the database in the current directory with relative path as key
-                var rootPath = Path.GetFullPath(".");
+                var rootPath = Directory.GetCurrentDirectory();
                 dbPath = Path.Combine(rootPath, BitCheckConstants.DatabaseFileName);
                 databaseKey = Path.GetRelativePath(rootPath, fullFilePath);
             }