creating and updating issues features

What if I wanted to change only the title?

From this implementation it looks like I need to pass in the values for all of the fields.

Here is an alternative way of defining these values such that not all are required.

```ruby
updates = {}
updates[:title] = title if title
updates[:body] = body if title
updates[:state] = state if state
updates[:labels] = labels if labesl
issue = github.issues.edit username, repo, number, updates
```