[Documentation] Fix misspelling of nil
[CHANGELOG] Grammar tuning and ensuring double spaces
[SpecHelper] Ensure that test UI is reset before each spec
[Analyzer] Improve handling of different types of duplicate dependencies
[Analyzer] Allow using CocoaPods with only externally-sourced dependencies in a   `Podfile` without specifying a source or displaying a warning

Closes https://github.com/CocoaPods/CocoaPods/issues/2735.
[Travis] Disable 2.0.0-p247 for now.

https://github.com/travis-ci/travis-ci/issues/2918
Un-deprecate use of implicit sources, by default all are used.

After much deliberation, the conclusion is that there is no good
techincal reason to enforce this, after all, and as such the decision
to deprecate it has been reverted.
[CONTRIBUTING] Add note calling on dev feelings.
[Error Report] Tell user to first read the CONTRIBUTING guide.
[Repo::Push] Clarify what repo an error is about.
[Repo::Push] show path of unclean repo

Closes https://github.com/CocoaPods/CocoaPods/issues/2753.
Merge pull request #2748 from CocoaPods/seg-duplicate-dependencies

[Analyzer] Improve handling of different types of duplicate dependencies
[ErrorReportSpec] Update test error report to include link to contributing guidelines

Update for https://github.com/CocoaPods/CocoaPods/commit/3a61c4a265d97c41bff17a2c3aeea878f228041b.
Revert "[Analyzer] Allow using CocoaPods with only externally-sourced dependencies in a   `Podfile` without specifying a source or displaying a warning"

This reverts commit 2cc9f01ddc7ebab7cf470d15cb0a4218f6bcfc99.

Follow-up to https://github.com/CocoaPods/CocoaPods/commit/7840787e05afb1da24bcfafa4a62f0de41ebf07a.

Conflicts:
	lib/cocoapods/installer/analyzer.rb
[AnalyzerSpec] Remove specs for implicit sources deprecation

Update for https://github.com/CocoaPods/CocoaPods/commit/7840787e05afb1da24bcfafa4a62f0de41ebf07a.
[XCConfigIntegrator] Assign xcconfigs to all targets being integrated.

Fixes #2752.
[Travis] Make autoload load `Xcodeproj::PlistHelper`.
[CHANGELOG] Tune grammar and fix spacing issues.
[Gemspec] Update xcodeproj dependency to `~> 0.20.1`
[Gemspec] Update cocoapods-try dependency to `~> 0.4.2`