bugfix: misunderstand the number of items perpage

[zhuangqh]

Signed-off-by: jerryzhuang zhuangqhc@gmail.com

Ⅰ. Describe what this PR did
The number of merged PR report by pouchrobot is different from expectations. This PR correct how to compute total number of merged PR.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

Ⅳ. Describe how to verify it

run this test code and compare it with the result from website toolbar manually.

package main

import (
	"fmt"
	"github.com/pouchcontainer/pouchrobot/server/gh"
)

var (
	repo = "pouch"
	owner = "alibaba"
)

func main() {
	ghClient := gh.NewClient(owner, repo, "")

	checkMergedPRFromDate(ghClient, "2018-05-14")
	checkMergedPRFromDate(ghClient, "2018-05-21")
}

func checkMergedPRFromDate(client *gh.Client, date string) {
	query := fmt.Sprintf("is:merged type:pr repo:%s/%s merged:>=%s", owner, repo, date)
	issueSearchResult, err := client.SearchIssues(query, nil, true)
	if err != nil {
		fmt.Println("fail to do request")
		return
	}

	fmt.Printf("%v merged pr since %s, actually get %v items\n",
		issueSearchResult.GetTotal(), date, len(issueSearchResult.Issues))
}

Ⅴ. Special notes for reviews

[allencloud]

LGTM