Try to fix spec failure on master

Updated CHANGELOG for #1978

* 'master' of https://github.com/apalancat/CocoaPods:
  Test and documentation for issue #1694
  Unset the `CDPATH` env variable before shelling-out. #1694

Conflicts:
	CHANGELOG.md

Make SourcesManager ignore some global git configs

Update changelog for #1704, #1840 & #1933

Merge branch 'fix_head_download_option' of https://github.com/neonichu/CocoaPods into neonichu-fix_head_download_option

Conflicts:
	spec/unit/installer/pod_source_installer_spec.rb

Updated CHANGELOG for #1958

Added changelog entry for pull #1960

Cleanup pod directory when download fails (probably due to a network error)

Conflicts:
	CHANGELOG.md

Fixes #1950.

Merge branch 'command-list-added-pod-versions' of https://github.com/z00b/CocoaPods into z00b-command-list-added-pod-versions

See https://travis-ci.org/CocoaPods/CocoaPods/jobs/21842661

Merge branch 'cleanup-pod-dir-on-failed-download' of https://github.com/alexrothenberg/CocoaPods into alexrothenberg-cleanup-pod-dir-on-failed-download

As requested in original PR (#1617).

Also remove some extraneous whitespace that crept in.

Use "gem install" instead of "gem update" in notice, as it is recommended

Fixes #1482

Changelog for 1721