Cocoapods: Fix issue <React/RCTConvert.h> not found

See #191.
Fixes issue <React/RCTConvert.h> by adding the missing dependency.

ReactNativePermissions.podspec

   s.preserve_paths         = 'LICENSE', 'package.json'
   s.source_files           = '**/*.{h,m}'
   s.exclude_files          = 'example/**/*'
+  s.dependency               'React'
 end