fixed backend path for CreateIssueComment

[Funzinator]

This fixes the wrong backend URL when creating issue comments.

[strk]

What bug does this fix ? How to reproduce the bug ?

[Funzinator]

Hi,
The issue is, that I can't add comments to issues in gitea.

Let me elaborate a bit further how to reproduce the issue (assuming url and token are filled accordingly with gitea installation details):

client := gitea.NewClient(url, token)
opt := gitea.CreateIssueOption{Title: "Test"}
issue, err := client.CreateIssue("funzi", "test", opt)
if err != nil {
	log.Println(err)
}
optC := gitea.CreateIssueCommentOption{Body: "Test Comment"}
comm, err := client.CreateIssueComment("funzi", "test", issue.Index, optC)
if err != nil {
	log.Println(err)
}
log.Printf("%v", comm)

This will print:

2017/03/12 22:58:17 404 Not Found
2017/03/12 22:58:17 &{0    <nil>  0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC}

The 404 Not Found is caused by the wrong backend URL "/repos/:%s/:%s/issues/%d/comments" which contains colons. If you change it to "/repos/%s/%s/issues/%d/comments" like I did in the pull request, it works fine.

[lunny]

LGTM

[appleboy]

LGTM