There is no version 4.x, yet, of symfony/monolog-bundle as of 23 Oct 2017.

Author: caciobanu

composer.json

@@ -37,7 +37,7 @@
         "doctrine/orm": "~2.3",
         "doctrine/doctrine-bundle": "~1.0",
         "symfony/monolog-bridge": "~2.3 || ~3.0 || ~4.0",
-        "symfony/monolog-bundle": "~2.3 || ~3.0 || ~4.0"
+        "symfony/monolog-bundle": "~2.3 || ~3.0 "
     },
     "autoload": {
         "psr-4": {