[DEPS] Also allow v2.0 of guzzlehttp/promises (#77)

Author: tPl0ch

composer.json

@@ -15,7 +15,7 @@
     "ext-curl": "*",
     "ext-json": "*",
     "guzzlehttp/guzzle": "^7.0",
-    "guzzlehttp/promises": "^1.4.0",
+    "guzzlehttp/promises": "^1.4.0|^2.0.0",
     "guzzlehttp/psr7": "^1.7|^2.1",
     "beberlei/assert": "~2.7|~3.0",
     "flix-tech/avro-php": "^5.0"