[Specification] Use string for all the keys

[fabiopelosin]

Currently the sub keys of the hashes use symbols (e.g. source the source params like :git). There is already logic there to handle the conversion when appropriate... but all the keys should be used as strings and converted, if needed, by the consumer.

This would also lead to a cleaner Lockfile:

EXTERNAL SOURCES:
  IFBKCampground:
    :git: https://github.com/irrationalfab/IFBKCampground.git
  IFBKThirtySeven:
    :path: ../../IFBKThirtySeven
  IRFAutoCompletionKit:
    :git: https://github.com/irrationalfab/IRFAutoCompletionKit
  IRFNavigationKit:
    :git: https://github.com/irrationalfab/IRFNavigationKit.git)

Related: CocoaPods/CocoaPods#1058 (comment)

@alloy we need to double check this for trunk because the JSON podspec return strings.

[alloy]

A string and a symbol are semantically (outside of Ruby) the same, so I don’t think it’s a real problem in trunk, unless I’m not understanding what you think the problem might be?

Maybe you can look into HashWithIndifferentAccess (from Activesupport) to see if it allows you to easily convert a Hash to a Hash with all symbol keys.

[fabiopelosin]

Actually this is not proving to be an issue, so I'm closing it until evidenced that this is needed is found.