Deprecation warning with webpack 4

[joelmukuthu]

Hi, there's a deprecation warning when this plugin is used with webpack 4:

DeprecationWarning: Tapable.plugin is deprecated. Use new API on `.hooks` instead
    at AngularGetTextPlugin.apply (node_modules/angular-gettext-plugin/index.js:39:12)
    at webpack (node_modules/webpack/lib/webpack.js:47:13)
    at processOptions (node_modules/webpack-cli/bin/cli.js:441:16)
    at yargs.parse (node_modules/webpack-cli/bin/cli.js:536:3)
    at Object.parse (node_modules/yargs/yargs.js:567:18)
    at node_modules/webpack-cli/bin/cli.js:219:8
    at Object.<anonymous> (node_modules/webpack-cli/bin/cli.js:538:3)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Module.require (module.js:587:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (node_modules/webpack/bin/webpack.js:155:2)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Function.Module.runMain (module.js:684:10)
    at startup (bootstrap_node.js:187:16)
    at bootstrap_node.js:608:3

Everything works still but it's likely that it'll stop working in a newer version of webpack.

Regards,
Joel