public function hardened() {
        $path = $this->path;

        $last = array_pop($path);

        if (strpos($last, "'") !== false) {
            return $this;
        }

        $last .= "'";

        $path[] = $last;

        return new static($path);
    }
public function hardened() {
        $path = $this->path;

        $last = array_pop($path);

        if (strpos($last, "'") !== false) {
            return $this;
        }

        $last .= "'";

        $path[] = $last;

        return new static($path);
    }
public function hardened ( ) { $ path = $ this -> path ; $ last = array_pop ( $ path ) ; if ( strpos ( $ last , "'" ) !== false ) { return $ this ; } $ last .= "'" ; $ path [ ] = $ last ; return new static ( $ path ) ; }
harden the last level of the path and return the new path

@return BIP32Path
harden the last level of the path and return the new path