Change indentation of package.json including Jest to 2 spaces

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Indentation of package.json including Jest is a hard tab. Since package.json generated by npm has two spaces, I want to make it the same.

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![package.json diff](https://cloud.githubusercontent.com/assets/12539/24228268/80421416-0fb6-11e7-9af3-d034c1756379.png)

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Closes https://github.com/facebook/react-native/pull/13099

Differential Revision: D4770208

Pulled By: ericnakagawa

fbshipit-source-id: 13f91068e40610473cd7b65e182a0fdc59af03ba

local-cli/init/init.js

@@ -113,7 +113,7 @@ function addJestToPackageJson(destinationRoot) {
   packageJSON.jest = {
     preset: 'react-native'
   };
-  fs.writeFileSync(packageJSONPath, JSON.stringify(packageJSON, null, '\t'));
+  fs.writeFileSync(packageJSONPath, JSON.stringify(packageJSON, null, 2));
 }
 
 module.exports = init;