Prepare 2.13.1 release

[ricellis]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [x] Added tests for code changes or test/build only changes
• [x] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Prepare for 2.13.1 release.

Approach

# 2.13.1 (2018-09-05)
- [FIXED] Regression that prevented `keys` being included as part of a `ViewMultipleRequest`.

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• N/A release PR

Monitoring and Logging

• "No change"