1.6.20
Update uglify-js-papandreou to 2.4.13-patch1.
minifySvgAssetsWithSvgo: Emit an 'info' event rather than 'warn' if svgo isn't found.

Also, mention npm in the message so that it's clearer how it's supposed to be installed.
mergeIdenticalAssets: Don't merge assets of different types.

This caused weird symptoms in buildProduction when a project contained both an empty stylesheet and an empty JavaScript file.
Update glob to 3.2.9.
1.6.21