Rename 0912-sort-an-array to 0912-sort-an-array.go

[Resolved PR comment] added file extension

Author: Sar-Go

go/0912-sort-an-array go/0912-sort-an-array.go

@@ -1,4 +1,4 @@
 func sortArray(nums []int) []int {
     sort.Ints(nums)
     return nums
-}
+}