Add psr-3 requirements in composer

Author: erickhun

composer.json

@@ -4,7 +4,8 @@
     "version": "0.1.0",
     "require": {
         "php": "^7.1",
-        "monolog/monolog": "1.25.*"
+        "monolog/monolog": "1.25.*",
+        "psr/log": "^1.1"
     },
     "require-dev": {
         "datadog/dd-trace": "0.34.*"