Release 0.18.1

* tag '0.18.1':
  Release 0.18.1
  [Fixtures] Update version
  [Changelog]
  Require Core 0.18.1
  Changelog [ci skip]
  [TargetIntegrator] Robustness against target with missing file references
  Fix Xcodeproj autoload
  More autoload #see 919
  Don't initialize Spec::Set::Statistics if not needed
  [Fix] Do not quote `$(inherited)`. Fixes #956.
  [SourceManagers] Fix CocoaPods spelling
  [Rakefile] Set git user on Travis 2
  [Rakefile] Set git user on Travis
  [Installer] Run the hooks of all the specs (not of the installed ones only)

Conflicts:
	CHANGELOG.md
	lib/cocoapods/command.rb