[ci skip] Add example for create a pull request.
Overload the #update_issue method to allow partial updates

The old argument structure still works as usual:

    update_issue(repo, number, title, body, options)

But now, you have the option of passing the title and body
attributes in the options hash (or omitting these attributes
if they should not be changed):

    update_issue(repo, number, options)
Merge pull request #531 from codetree/allow-partial-issue-updates

Overload the #update_issue method to allow partial updates
Fix link to pessimistic versioning explanation in README

Fixes #532
[skip ci]
Merge pull request #527 from JuanitoFatas/doc/create-pr-example

[ci skip] Add example for create a pull request.
Fix typo in documentation

:sparkling_heart:
Merge pull request #533 from davidcelis/patch-1

Fix typo in documentation

[ci skip]
Remove Deployments API preview warnings
Setting rate_limit resets_in to 0 if it goes negative
Making rate_limit resets_in positive cooercion more succinct per @pengwynn's feedback
Merge pull request #536 from markphelps/resets_in_should_not_be_negative

Setting rate_limit resets_in to 0 if it goes negative
Merge pull request #537 from octokit/remove-deployments-preview-warning

Remove Deployments API preview warnings
Bump sawyer
v3.6.0
Release 3.6.0