Allow psr/cache 2.0 as well as 1.0

Author: johnnoel

composer.json

@@ -24,7 +24,7 @@
         "php-http/discovery": "^1.12",
         "php-http/httplug": "^2.2",
         "php-http/multipart-stream-builder": "^1.1.2",
-        "psr/cache": "^1.0",
+        "psr/cache": "^1.0|^2.0",
         "psr/http-client-implementation": "^1.0",
         "psr/http-factory-implementation": "^1.0",
         "psr/http-message": "^1.0",