add Solution 70 [golang]

Author: lightfish-zhang

solution/0070.Climbing Stairs/Solution.go

@@ -0,0 +1,10 @@
+func climbStairs(n int) int {
+	if n < 3 {
+		return n
+	}
+	x, y := 1, 2
+	for i := 2; i < n; i++ {
+		x, y = y, x+y
+	}
+	return y
+}