PullRequestCommit Author and Committer fields were mistakenly typed with
Committer when they should be of type User.
Previously the types of properties were:
* `PullRequestCommit.Author/Committer`: `Committer`
* `Commit.Author/Committer`: `Committer`
Correct types should be:
* `PullRequestCommit.Author/Committer`: `User`
* `Commit.Author/Committer`: `Committer`
These fields always fail to deserialize in the API calls but produce no
errors, only objects with default values.