title: Enzyme not working with karma + webpack
body: <p>I am trying to add Enzyme to my project. When I attempt to run <code>karma start</code> I get the error <code>Module build failed: Error: Couldn't find preset "airbnb" relative to directory "/Users/kieran/IdeaProjects/tahrir</code>. I have run <code>npm i --save-dev enzyme</code>. My <code>karma.conf.js</code> looks like</p>
  
  <pre><code>module.exports = function (config) {
      config.set({
          browsers: ['Chrome'],
          singleRun: true,
          frameworks: ['jasmine'],
          files: [
              {pattern: 'tests.webpack.js'}
          ],
          preprocessors: {
              'tests.webpack.js': ['webpack', 'sourcemap']
          },
          reporters: ['dots'],
          webpack: {
              devtool: 'inline-source-map',
              module: {
                  loaders: [
                      {
                          test: /\.js$/,
                          exclude: /\/node_modules\//,
                          loader: 'babel',
                          query: {
                              presets: ['airbnb']
                          }
                      }
                  ]
              },
              externals: {
                  'cheerio': 'window',
                  'react/addons': true,
                  'react/lib/ExecutionEnvironment': true,
                  'react/lib/ReactContext': true
              }
          },
          webpackServer: {
              noInfo: true
          }
      });
  };
  </code></pre>
  
  <p>Is there something else I need to add so that webpack can access the airbnb present?</p>