Update version in package.json to 0.6.0

Summary:
The version in master should at least match the latest rc's version.
Closes https://github.com/facebook/react-native/pull/1599
Github Author: James Ide <ide+github@jameside.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-native",
-  "version": "0.4.4",
+  "version": "0.6.0",
   "description": "A framework for building native apps using React",
   "license": "BSD-3-Clause",
   "repository": {