Declare compatibility with Monolog v2

This is required when using this extension with MediaWiki 1.36. None of
the breaking changes in Monolog 2.0.0 should affect this extension, as
far as I can tell.

Author: lucaswerkmeister

composer.json

@@ -14,7 +14,7 @@
 	"require": {
 		"php": ">=5.5.0",
 		"benestar/asparagus": "~0.4",
-		"monolog/monolog": "~1.18",
+		"monolog/monolog": "~1.18||^2.0.0",
 		"wikibase/data-model": "~6.0|~7.0|~8.0|~9.0"
 	},
 	"autoload": {