Update behat/behat requirement in /build/integration

Updates the requirements on [behat/behat](https://github.com/Behat/Behat) to permit the latest version.
- [Release notes](https://github.com/Behat/Behat/releases)
- [Changelog](https://github.com/Behat/Behat/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Behat/Behat/compare/v3.7.0...v3.8.0)

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

build/integration/composer.json

@@ -1,7 +1,7 @@
 {
   "require-dev": {
     "phpunit/phpunit": "~6.5",
-    "behat/behat": "~3.7.0",
+    "behat/behat": "~3.8.0",
     "guzzlehttp/guzzle": "6.5.2",
     "jarnaiz/behat-junit-formatter": "^1.3",
     "sabre/dav": "3.2.3",