By Aishwarya Nair (Reuters) – General Motors Co outsold Japanese automaker Toyota Motor Corp in the United States in the third quarter, data on Monday showed, but analysts and investors are fretting that a darkening economic picture will lead to a drop in future car sales. GM said it sold 555,580 vehicles in the quarter through September, 24% higher than last year when inventory shortages hit sales. Toyota’s sales fell 7.1% to 526,017 vehicles in the same period. The Detroit automaker added it would boost production of its Chevrolet Bolt electric models in response to higher demand. Thus far, …