simplify and combine karma file patterns

config/karma.config.js

@@ -8,20 +8,13 @@ module.exports = function(config) {
     basePath: ROOT_PATH,
     frameworks: ['jquery-2.1.0', 'jasmine'],
     files: [
-      'spec/javascripts/*_spec.js',
-      'spec/javascripts/*_spec.js.es6',
-      { pattern: 'spec/javascripts/fixtures/**/*.html', included: false, served: true },
-      { pattern: 'spec/javascripts/fixtures/**/*.json', included: false, served: true },
+      'spec/javascripts/**/*_spec.js?(.es6)',
+      { pattern: 'spec/javascripts/fixtures/**/*@(.json|.html|.html.raw)', included: false },
     ],
     preprocessors: {
-      'spec/javascripts/*_spec.js': ['webpack'],
-      'spec/javascripts/*_spec.js.es6': ['webpack'],
-      'app/assets/javascripts/**/*.js': ['webpack'],
-      'app/assets/javascripts/**/*.js.es6': ['webpack'],
+      'spec/javascripts/**/*_spec.js?(.es6)': ['webpack'],
     },
-
     webpack: webpackConfig,
-
     webpackMiddleware: { stats: 'errors-only' },
   });
 };