prepare 6.1.6 release

[LaunchDarklyCI]

[6.1.6] - 2021-04-23

Fixed:

• In automatic configuration mode, if a new credential was created for an already-configured environment (for instance, by using "reset SDK key" on the LaunchDarkly dashboard), the Relay Proxy did not accept subsequent SDK requests using the new credential until the next time the Relay Proxy was started. The symptom was that the SDK endpoints would return a 404 status instead of 200 (even though unknown credentials normally receive a 401). Also, if an SDK key or mobile key had already been changed prior to starting the Relay Proxy, but the older key had not yet expired, the Relay Proxy was not recognizing the old key in requests. Both of these problems have been fixed.
• Fixed a broken link in the Metrics documentation page. (Thanks, natashanwright!)