Update guzzlehttp/guzzle from 6.5.3 to 6.5.4

[violinist-bot]

If you have a high test coverage index, and your tests for this pull request are passing, it should be both safe and recommended to merge this update.

Here is a list of changes between the version you use, and the version this pull request updates to:

• a4a1b693 Adding changelog for 6.5.4 (#2651)
• 0d137e94 [6.5] Remove obsolete statement in handler option docs (#2567)
• d3f2c179 [6.5] Fix various intl icu issues (#2626)
• c8162bee Fix use and phpDoc for @throws GuzzleException/InvalidArgumentException (#2621)
• 5262ecfd Document the impact of fixing time units for RetryMiddleware (#2570)
• 351a213b Fix "Fixed deprecation warning in node test server" (#2638)

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[coveralls]

Coverage remained the same at 99.038% when pulling f83a523 on violinist-dev:guzzlehttpguzzle653654 into 7ba050b on typhonius:master.