Added compatibility with newer versions of psr/log

composer.json

@@ -9,7 +9,7 @@
 		"doctrine/common" : ">=2.6.1",
 		"doctrine/cache" : "1.*",
 		"guzzlehttp/guzzle" : ">=6.0",
-		"psr/log": "^1.1",
+		"psr/log": ">=1.1",
 		"kevinrob/guzzle-cache-middleware": "^3.2",
 		"webmozart/assert": "^1.6"		
 	},