making it work with webpack compression plugin (#18)
making it work with webpack compression plugin (#18)

Support webpack compression plugin

webpack compression plugin use the phase 'compilation.optimize-assets' so we should use the phase 'compilation.optimize-chunk-assets'

* using LastCallWebpackPlugin.PHASE.OPTIMIZE_CHUNK_ASSETS

* using LastCallWebpackPlugin.prototype.PHASE.OPTIMIZE_CHUNK_ASSETS

NMFR/optimize-css-assets-webpack-plugin