Fix CommentToken for parsing comment when multi-line comments appear in the single-line comment

In current version, we cannot parse following code.
This pull request support parsing comment when multi-line comments appear in the single-line comment.

```
$ cat hoge.green
int f() {
    // assert(n == 1)// */
}
```

```
$ java -jar GreenTeaScript.jar hoge.green
(error) (hoge.green:1) expected name; given = {
(info) (hoge.green:2) skipping:
(info) (hoge.green:2) skipping: /
(info) (hoge.green:2) skipping: /
(info) (hoge.green:2) skipping: assert
(info) (hoge.green:2) skipping: (
(info) (hoge.green:2) skipping: n
(info) (hoge.green:2) skipping: ==
(info) (hoge.green:2) skipping: 1
(info) (hoge.green:2) skipping: )
(info) (hoge.green:2) skipping: /
(info) (hoge.green:2) skipping: /
(info) (hoge.green:2) skipping: *
(info) (hoge.green:2) skipping: /
(info) (hoge.green:3) skipping:
(info) (hoge.green:3) stopping script eval at }
abort loading: hoge.green
```