LAGOS (Reuters) - Nigeria's naira gained 1.26 percent against the dollar on Friday on the back of intervention by the central bank and dollar sales by a unit of Chevron. The local currency closed at 179.6 to the dollar, firmer than 181.90 the naira closed at the previous day. Traders said the central bank sold dollars to some lenders just before the close of trading on Friday. Chevron sold $57 million to some lenders. Nigeria's currency has been trading within a range of 180-182 to the dollar since last week, as central bank regular intervention has helped keep it afloat. It remains outside the bank's target band of 5 percent plus or minus 168 to the dollar since last month's devaluation. The forex reserves of Africa's biggest crude exporter are down to about $35.88 billion, their lowest since July 2012, on the frequent intervention in the interbank forex market by the central bank.