support asset modules with generator

[hanzhangyu]

add generator config to custom asset filename will throw UnhandledPromiseRejectionWarning: TypeError: config.module.rule(...).test(...).type(...).generator is not a function

config.modules
    .rule('fonts')
    .test(/\.tff$/)
    .type('asset')
    .generator({
      filename: 'fonts/[hash][ext][query]',
    })
    .parser({
      dataUrlCondition: {
        maxSize: 4 * 1024,
      },
    });

[UNDERCOVERj]

why nobody reviews

[edmorley]

Closing since this project is no longer maintained:
#358