Fix indent for .babelrc in HelloWorld template

Summary:
Minor code formatting.
Each time I run `react-native init` I must reindent this file.
Closes https://github.com/facebook/react-native/pull/12850

Differential Revision: D4691374

fbshipit-source-id: dc02b021e2f320f1046e4e6d024ba675a4213de8

local-cli/templates/HelloWorld/_babelrc

@@ -1,3 +1,3 @@
 {
-"presets": ["react-native"]
-}
+  "presets": ["react-native"]
+}