* Add a trailing slash to URL when updating or deleting a file.
* Update test files to match new create/update/delete_file Repo methods
* Add trailing slash to get_contents() method
* update tests
* add missing slash in get_dir_contents
* add example usage
* remove dup slashes in tests
* clarify example comments
## What does this change do?
Adds a small example of how to get at the date a commit took place.
### Changes
#### doc/examples/Commit.rst
Adds a block of code that demonstrates how to get at a commit's date.
## Motivation
This example is in the spirit of #874.
When I began using PyGithub it was not readily apparent to me where the commit date was being abstracted to. Being unfamiliar with Git's API, it took some convincing for me to be satisfied that the `Commit.commit.author/committer.date` path would get me the commit date.
I would hope that this would save somebody a little bit of time in the future.
## How has this been tested?
I've built the docs locally and made sure the HTML is generated as expected.
## Screenshots
This PR add the follow code examples
* Issue examples (get list, get specific issue, create issue)
* Milestone examples (get list, get specific milestone, create milestone)
Ref.: https://github.com/PyGithub/PyGithub/issues/874
Juri Di Rocco
