added solution in golang: 41. First Missing Positive

Signed-off-by: rajput-hemant <rajput.hemant2001@gmail.com>

Author: rajput-hemant

src/0001-0100/041 - First Missing Positive/first_missing_positive.go

@@ -0,0 +1,21 @@
+package main
+
+func firstMissingPositive(nums []int) int {
+	i := 0
+
+	for i < len(nums) {
+		if nums[i] > 0 && nums[i] <= len(nums) && nums[nums[i]-1] != nums[i] {
+			nums[nums[i]-1], nums[i] = nums[i], nums[nums[i]-1]
+		} else {
+			i++
+		}
+	}
+
+	for i, num := range nums {
+		if num != i+1 {
+			return i + 1
+		}
+	}
+
+	return len(nums) + 1
+}