Recommended settings for uglify.minify()

[rwaldron]

In mishoo/UglifyJS#968 (comment), @kzc recommends adding the following settings for even more code reduction wins:

    compress: {
        ecma: 6,
        passes: 3,
        pure_getters: true,
        // other existing options
    },
    output: {
        ecma: 6,
        // other existing options
    },

I think pure_getters might be problematic, but still worth trying!

[rwaldron]

We landed this

[kzc]

@rwaldron Did you see any deploy size reduction?