Feature flags always returns TRUE

[lenage]

In example:

var definePlugin = new webpack.DefinePlugin({
  __DEV__: JSON.stringify(JSON.parse(process.env.BUILD_DEV || 'true')),
  __PRERELEASE__: JSON.stringify(JSON.parse(process.env.BUILD_PRERELEASE || 'false'))
});

__DEV__ always be true even i BUILD_DEV is undefined.

JSON.stringify(JSON.parse(process.env.BUILD_DEV || 'true')) => 'true'

maybe we should update this example to make __DEV__ return true only when BUILD_DEV exist.

for example:

JSON.stringify(typeof(process.env.BUILD_DEV) !== undefined)

[colinrymer]

I also noticed this when reading through the README.