Add tasks for all the new languages

Task/Fibonacci-sequence/Swift/fibonacci-sequence-2.swift

@@ -0,0 +1,11 @@
+func fibonacci(n: Int) -> Int {
+    if n < 2 {
+        return n
+    }
+    var fibPrev = 1
+    var fib = 1
+    for num in 2...n {
+        (fibPrev, fib) = (fib, fib + fibPrev)
+    }
+    return fib
+}