react/prefer-stateless-function works different than described in docs

For the react/prefer-stateless-function rule the docs for ignorePureComponents option states:

When true the rule will ignore Components extending from React.PureComponent that use this.props or this.context.

Actually it also ignore every PureComponent that use not only props or context, but ignores every component that use this. If this is not intended I prepared a fix (GH-1902), otherwise it makes sense to update the docs.