Merge pull request #2 from noxify/master

Support for CommonMark 0.18

Author: johnnyhuy

composer.json

@@ -22,7 +22,7 @@
         "php": "^7.1.3",
         "ext-json": "*",
         "laravel/framework": "5.6.*|5.7.*",
-        "league/commonmark": "^0.17"
+        "league/commonmark": "^0.17|^0.18"
     },
     "require-dev": {
         "mockery/mockery": "^1.1",