Preheat oven to 325°F. Line a standard 12-cup cupcake tin with paper baking cups. To make the cupcakes, mix together the rice milk and apple cider vinegar in a 2-cup measuring cup. Whisk together the flour, cacao powder, baking powder, baking soda, guar gum and salt in a large bowl. Make a well in the middle. Add the grapeseed oil, coconut nectar, vanilla and stevia to the flour mixture and stir to combine. Next add the rice milk mixture and stir until the liquid is absorbed and the batter is smooth. Stir in the yogurt until well combined. Pour the batter into the measuring cup, as the spout will make it easier to pour the batter into the cupcake tin without spillage. Pour the batter into the prepared cupcake tin, dividing it evenly. Each cup should be about two-thirds full. Bake the cupcakes for 16 to 17 minutes, or until they bounce back slightly to the touch. Rotate the cupcake tin from front to back after 10 minutes of baking.