Chipotle is going through a big change right now, and investors are worried. If you think long term, this could be a chance to buy.Chipotle Mexican Grill (CMG -1.28%) has become one of the most prominent fast-casual restaurant brands in the world. But all companies, no matter how well consumers like them, cycle between good and bad times. With Chipotle's stock down around 15% from its 52-week high, long-term growth investors might want to jump aboard. And, yes, there are some negatives to understand before ...