Added support draft pull request for github

github/payload.go

@@ -3589,6 +3589,7 @@ type PullRequestPayload struct {
 		Assignee           *Assignee   `json:"assignee"`
 		Assignees          []*Assignee `json:"assignees"`
 		Milestone          *Milestone  `json:"milestone"`
+		Draft              bool        `json:"draft"`
 		CommitsURL         string      `json:"commits_url"`
 		ReviewCommentsURL  string      `json:"review_comments_url"`
 		ReviewCommentURL   string      `json:"review_comment_url"`

testdata/github/pull-request.json

@@ -39,6 +39,7 @@
     "merge_commit_sha": null,
     "assignee": null,
     "milestone": null,
+    "draft": false,
     "commits_url": "https://api.github.com/repos/baxterthehacker/public-repo/pulls/1/commits",
     "review_comments_url": "https://api.github.com/repos/baxterthehacker/public-repo/pulls/1/comments",
     "review_comment_url": "https://api.github.com/repos/baxterthehacker/public-repo/pulls/comments{/number}",