Gender-neutralise podfile.rb docs

[ci skip]

Deprecate `dependency' in favor of `pod' in Podfile

* 'develop' of github.com:CocoaPods/CocoaPods:
  [Rakefile] Release from develop branch.

Conflicts:
	Rakefile

* 'master' of github.com:CocoaPods/CocoaPods:
  Array#flatten! returns nil if no modifications were made (i.e., array contains no subarrays.)

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