Fix cakephp constraint.

Author: markstory

composer.json

@@ -24,7 +24,7 @@
     },
     "require": {
         "php": ">=5.6.0",
-        "cakephp/cakephp": "dev-3.next as 3.6.0",
+        "cakephp/cakephp": "^3.6.0",
         "cakephp/chronos": "^1.0.0",
         "cakephp/plugin-installer": "^1.0.0",
         "composer/composer": "^1.3.0",