Enable static and instance fields in flow

No need for the suppression comment.

.flowconfig

@@ -22,4 +22,5 @@ src
 interfaces
 
 [options]
-suppress_comment= \\(.\\|\n\\)*\\$FlowStaticPropertyWarning
+esproposal.class_static_fields=enable
+esproposal.class_instance_fields=enable

src/components/style-sheet.js

@@ -5,7 +5,6 @@ import React, {Component} from 'react';
 import StyleKeeper from '../style-keeper';
 
 export default class StyleSheet extends Component {
-  // $FlowStaticPropertyWarning
   static contextTypes = {
     _radiumStyleKeeper: React.PropTypes.instanceOf(StyleKeeper)
   };