Fix missing getChildContext lifecycle method in prefer-stateless-function (fixes #492)

Author: yannickcr

docs/rules/prefer-stateless-function.md

@@ -6,7 +6,7 @@ Stateless functional components are more simple than class based components and
 
 This rule will check your class based React components for
 
-* lifecycle methods: `state`, `getInitialState`, `componentWillMount`, `componentDidMount`, `componentWillReceiveProps`, `shouldComponentUpdate`, `componentWillUpdate`, `componentDidUpdate` and `componentWillUnmount`
+* lifecycle methods: `state`, `getInitialState`, `getChildContext`, `componentWillMount`, `componentDidMount`, `componentWillReceiveProps`, `shouldComponentUpdate`, `componentWillUpdate`, `componentDidUpdate` and `componentWillUnmount`
 * usage of `this.setState`
 * presence of `ref` attribute in JSX
 

lib/rules/prefer-stateless-function.js

@@ -17,6 +17,7 @@ module.exports = Components.detect(function(context, components, utils) {
   var lifecycleMethods = [
     'state',
     'getInitialState',
+    'getChildContext',
     'componentWillMount',
     'componentDidMount',
     'componentWillReceiveProps',