Update dependency guzzlehttp/promises to v2

Author: renovate[bot]

composer.json

@@ -18,7 +18,7 @@
         "php": "^7.1 || ^8.0",
         "composer/package-versions-deprecated": "1.11.99.2",
         "elife/api-client": "^1.0",
-        "guzzlehttp/promises": "^1.0",
+        "guzzlehttp/promises": "^2.0",
         "guzzlehttp/psr7": "^1.0",
         "symfony/serializer": "^2.8.2 || ^3.0.2"
     },