math: Type Conversion of Inf(1) to int produces a negative integer instead of a positive one

```go
package main

import (
	"fmt"
	"math"
)

func main() {
	fmt.Println("Hello, playground")
	m := int(math.Inf(1))
	fmt.Println(m)
}

```
[go playground](https://play.golang.org/p/qAx6d8h5Hzg)

### What did you expect to see?

I expected to see positive infinity representation or  9223372036854775807

### What did you see instead?
 -9223372036854775807