Use MixedCase constant names

See https://github.com/golang/go/wiki/CodeReviewComments#mixed-caps

routers/repo/pull.go

@@ -687,7 +687,7 @@ func CompareAndPullRequestPost(ctx *context.Context, form auth.CreateIssueForm)
 		HeadRepo:     headRepo,
 		BaseRepo:     repo,
 		MergeBase:    prInfo.MergeBase,
-		Type:         models.PULL_REQUEST_GITEA,
+		Type:         models.PullRequestGitea,
 	}
 	// FIXME: check error in the case two people send pull request at almost same time, give nice error prompt
 	// instead of 500.

routers/repo/webhook.go

@@ -383,7 +383,7 @@ func TestWebhook(ctx *context.Context) {
 		Pusher: apiUser,
 		Sender: apiUser,
 	}
-	if err := models.PrepareWebhooks(ctx.Repo.Repository, models.HOOK_EVENT_PUSH, p); err != nil {
+	if err := models.PrepareWebhooks(ctx.Repo.Repository, models.HookEventPush, p); err != nil {
 		ctx.Flash.Error("PrepareWebhooks: " + err.Error())
 		ctx.Status(500)
 	} else {