Fix fields of GHRepository

[wolfogre]

According to the lasted version of https://developer.github.com/v3/repos/#get , the fields of GHRepository need be fixed:

• Add new field has_pages ;
• Add new field stargazers_count, Be careful, Pull request Add stargarzer field to GHRepository #301 did the same thing
• Rename forks to forks_count, forks still works, but you can't see it in the newest docs;
• Rename watchers to watchers_count, watchers still works, but you can't see it in the newest docs;
• Rename open_issues to open_issues_count, open_issues still works, but you can't see it in the newest docs;
• Delete network_count, I am not sure what it means, but it is always same as forks_count, and of coursed you can't see it in the newest docs;

I did some basic tests, this is the result:

kohsuke/github-api:
hasPages:true
getForksCount:241
getStargazersCount:307
getWatchersCount:307
getOpenIssueCount:17

You may notice that the watchers_count is same as stargazers_count, it is not a bug in my code, you can see the same situation in the docs, and the subscribers_count is the real watcher count.