upgrade psr/log (#8)

Authored-by: Xavier Marchegay <xmarchegay@clever-age.com>

Author: xaviermarchegay

composer.json

@@ -24,7 +24,7 @@
         "payum/core": "^1.5",
         "symfony/options-resolver": ">3.4,<7.0",
         "symfony/process": ">3.4,<7.0",
-        "psr/log": "^1.0"
+        "psr/log": "^1.0|^2.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^7.0|^8.0",