Add OpenBSD for `LookPath' function.

[lu4nx]

Hi, Nuclei's Headless feature relies on the go-rod library and looks for Chrome executables via the LookPath function, but it could not be found in OpenBSD, so I added the patch.

The following is some of the information in OpenBSD:

$ cat hi.go                                                                                                                                                                                            
package main

import (
	"fmt"
	"runtime"
)

func main() {
	fmt.Println(runtime.GOOS)
}
$ go run hi.go 
openbsd
$ whereis chrome
/usr/local/bin/chrome
$ uname -a
OpenBSD my-openbsd 7.3 GENERIC.MP#1125 amd64