(Reuters) - Alphabet Inc-owned Google will buy wearable device maker Fitbit Inc for $2.1 billion (£1.62 billion), as the search giant looks to enter the fast-growing market for fitness trackers and smartwatches.Fitbit said on Friday it had been offered $7.35 per share in cash, a premium of about 19% to the stock's closing price on Thursday. Fitbit shares have gained more than 40% since Reuters exclusively reported on Monday that Google had made an offer for the maker of the popular colourful..