Change React version to 15.3.1 (no more RC)

Summary:
React 15.3.1 has been published; stop using the RC.
Closes https://github.com/facebook/react-native/pull/9783

Reviewed By: bestander

Differential Revision: D3876515

Pulled By: mkonicek

fbshipit-source-id: 2ad990b55359e445dad9119b7434930c0cc72eda

package.json

@@ -132,7 +132,7 @@
     "react-native": "local-cli/wrong-react-native.js"
   },
   "peerDependencies": {
-    "react": "15.3.1-rc.2"
+    "react": "~15.3.1"
   },
   "dependencies": {
     "absolute-path": "^0.0.0",
@@ -217,7 +217,7 @@
     "jest-runtime": "15.1.0",
     "mock-fs": "^3.11.0",
     "portfinder": "0.4.0",
-    "react": "15.3.1-rc.2",
+    "react": "~15.3.1",
     "shelljs": "0.6.0",
     "sinon": "^2.0.0-pre.2"
   }