Adding "generateSourceMaps" break uglify's beautify option #969

Hello,

I'm using requirejs to build all my sources into a single file.
I have two build, one for development (no compress, no mangle and source map) and one for production.

When I add the "generateSourceMaps" option, the generated file is being compress no matter what others options I set.

Here's my configuration :

options: {
    baseUrl: "src/js/",
    // generateSourceMaps: true, // adding this one output a minified file
    name: "loader",
    out: "dist/js/script.js",
    uglify: {                    // despite those options
        mangle: false,
        output: {
            beautify: true
        },
    }
}