build(deps): bump php-http/httplug from 2.1.0 to 2.2.0

Bumps [php-http/httplug](https://github.com/php-http/httplug) from 2.1.0 to 2.2.0.
- [Release notes](https://github.com/php-http/httplug/releases)
- [Changelog](https://github.com/php-http/httplug/blob/master/CHANGELOG.md)
- [Commits](php-http/httplug@2.1.0...2.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

composer.json

@@ -16,7 +16,7 @@
         "php": "^7.1",
         "ext-json": "*",
         "php-http/client-implementation": "^1.0",
-        "php-http/httplug": "^2.0",
+        "php-http/httplug": "^2.2",
         "psr/http-factory": "^1.0"
     },
     "require-dev": {