Gitbook 2.0.1 compatibility

Contributor: @todvora

---

Gitbook 2.0.1 has removed page:after hook which this plugin needs. An issue has been reported here - GitbookIO/gitbook#724 but meanwhile this plugin is using workaround added by this pull request - #4

So when using Gitbook 2.0.1, you may see following warning in console at the time of running build:

warn: hook 'page' used by plugin 'gitbook-plugin-edit-link' is deprecated, and will be remove in the coming versions

You can safely ignore above warning for now.