Every year we at Entrepreneur publish our fastest growing franchises ranking. You might expect to see a bunch of new and trendy brands on such a list, but as it turns out, most of the fastest-growing franchises aren’t flashes in the pan; they’re companies that have learned how to sustain their growth over years and even decades. In fact, the average company on the list has been franchising for 24 years. And this year’s number one, Dunkin’ Donuts, has been going strong for 62 years, with no signs…