style: simplify fib_iterative (#188)

* tests: add missing test case for `fib_iterative`

* style: remove redundant brach in `fib_iterative`

Author: vil02

src/math/fibonacci.jl

@@ -98,8 +98,6 @@ function fib_iterative(n::Int)
         throw(DomainError("n is negative"))
     elseif n == 1
         return [0]
-    elseif n == 2
-        return [0, 1]
     else
         result = [0, 1]
         a, b = 0, 1

test/math.jl

@@ -239,6 +239,7 @@ using TheAlgorithms.Math
         @test fib_recursive_memo(6) == [0, 1, 1, 2, 3, 5]
         @test_throws DomainError fib_recursive_memo(-1)
         @test fib_iterative(1) == [0]
+        @test fib_iterative(2) == [0, 1]
         @test fib_iterative(6) == [0, 1, 1, 2, 3, 5]
         @test_throws DomainError fib_iterative(-1)
     end