Fix regression in StyleSheet.setStyleAttributePreprocessor (facebook#22262)

Summary:
This regression was caused by 199c918 - property values are initialized to true rather than a string that matches the property name now.
Pull Request resolved: facebook#22262

Differential Revision: D13048839

Pulled By: hramos

fbshipit-source-id: 09471334c37f3930aae7e35066943f33f8e617e5

Author: brentvatne

Libraries/StyleSheet/StyleSheet.js

@@ -339,7 +339,7 @@ module.exports = {
   ) {
     let value;
 
-    if (typeof ReactNativeStyleAttributes[property] === 'string') {
+    if (ReactNativeStyleAttributes[property] === true) {
       value = {};
     } else if (typeof ReactNativeStyleAttributes[property] === 'object') {
       value = ReactNativeStyleAttributes[property];