Overwrite default_args with costome_args

[lishimeng]

func New(url, dir string, width, height int, customArgs ...string) (UI, error) {
...
args := append(defaultChromeArgs, fmt.Sprintf("--app=%s", url))
args = append(args, fmt.Sprintf("--user-data-dir=%s", dir))
args = append(args, fmt.Sprintf("--window-size=%d,%d", width, height))
args = append(args, customArgs...)
args = append(args, "--remote-debugging-port=0")

**args = handleArgs(args) // override default args with custome args** 

chrome, err := newChromeWithArgs(ChromeExecutable(), args...)
...

}

func handleArgs(src []string) (dest []string) {
m := make(map[string]bool)
for _, s := range src {
m[s] = true
}
for s, _ := range m {
dest = append(dest, s)
}
return
}