Fix passing react native path in Podfile template (#29285)

Summary:
Since react-native-community/cli@e949e23#diff-d1800049b92343288bcbc1c484575058 the RN cli script returns an object with `:reactNativePath` instead of just JSON. Not super familiar with how objects / JSON works in ruby but using this syntax instead works.

## Changelog

[Fixed] [iOS] - Fix passing react native path in Podfile template

Pull Request resolved: #29285

Test Plan: Tested in a project inside a monorepo using the latest version of RN CLI that the proper react-native path is now passed.

Reviewed By: fkgozali

Differential Revision: D23941162

Pulled By: hramos

fbshipit-source-id: 0115412ec6d6bca101612d760dfc00cf89d97f1e

Author: janicduplessis

template/ios/Podfile

@@ -6,7 +6,7 @@ platform :ios, '10.0'
 target 'HelloWorld' do
   config = use_native_modules!
 
-  use_react_native!(:path => config["reactNativePath"])
+  use_react_native!(:path => config[:reactNativePath])
 
   target 'HelloWorldTests' do
     inherit! :complete