Panic when linenostart is a string

[jmooring]

markdown

~~~text {linenostart="1"}
foo
~~~

code

package main

import (
	"bytes"
	"fmt"

	"github.com/yuin/goldmark"
	highlighting "github.com/yuin/goldmark-highlighting"
)

func main() {
	md := goldmark.New(
		goldmark.WithExtensions(
			highlighting.Highlighting,
		),
	)

	input := `
~~~text {linenostart="1"}
foo
~~~
`

	var buf bytes.Buffer
	if err := md.Convert([]byte(input), &buf); err != nil {
		panic(err)
	}

	fmt.Println(buf.String())

}