Issue #2348365 by larowlan | mtdowling: Update to Guzzle 5.

composer.json

composer.lock

core/modules/update/src/UpdateFetcher.php

core/vendor/composer/autoload_files.php

core/vendor/composer/autoload_psr4.php

core/vendor/composer/installed.json

core/vendor/guzzlehttp/guzzle/.gitignore

core/vendor/guzzlehttp/guzzle/.travis.yml

core/vendor/guzzlehttp/guzzle/CHANGELOG.md

core/vendor/guzzlehttp/guzzle/Makefile

core/vendor/guzzlehttp/guzzle/README.md

core/vendor/guzzlehttp/guzzle/UPGRADING.md

core/vendor/guzzlehttp/guzzle/build/packager.php

core/vendor/guzzlehttp/guzzle/composer.json

core/vendor/guzzlehttp/guzzle/docs/adapters.rst

core/vendor/guzzlehttp/guzzle/docs/clients.rst

core/vendor/guzzlehttp/guzzle/docs/conf.py

core/vendor/guzzlehttp/guzzle/docs/events.rst

core/vendor/guzzlehttp/guzzle/docs/faq.rst

core/vendor/guzzlehttp/guzzle/docs/handlers.rst