Preheat oven to 400 degrees. In a bowl, combine flour, sugar, cocoa, baking powder, baking soda, and salt. Make a well in the center. dd oil, vanilla, vinegar, and warm water. Stir just until moist. Add hocolate chips. Spoon batter into prepared muffin tin (use cupcake papers), filling 0.75 full. Bake for 15 20 minutes.