Prepare 3.6.1 release

[felixarntz]

This issue is about publishing the Performance Lab 3.6.1 release, a hot fix to only include #1660 / #1675.

No other plugins will be released as part of this extra "cycle".

[felixarntz]

@eclarke1 @westonruter @joemcgill FYI just created this issue. Would you be okay that I publish the new version including the fix tomorrow? I have already verified that it works as expected.

[felixarntz]

Release branch: https://github.com/WordPress/performance/tree/release/3.6.1
Release preparation PR: #1678

[westonruter]

@felixarntz Go for it!