CommandBugReport stores id, but needs to store number

[JnCrMx]

In this line, CommandBugReport stores the ID of the issue in the database for notifications:

https://github.com/JnCrMx/ChocoBot/blob/b2e6cf9f0ed03c0e0fb482ca7ece79727af03571/src/main/java/de/jcm/discord/chocobot/command/CommandBugReport.java#L60

It turns out that not the ID, but the number of the issue is required to poll events. Therefore change this to store the number instead of the ID.

See:

GET /repos/:owner/:repo/issues/:issue_number/events

in https://developer.github.com/v3/issues/events/

and

"events_url": "https://api.github.com/repos/octocat/Hello-World/issues/1347/events",
"html_url": "https://github.com/octocat/Hello-World/issues/1347",
"number": 1347,
"state": "open",
"title": "Found a bug",

in https://developer.github.com/v3/issues/