Proper version constraint on maknz/slack

composer.json

@@ -10,8 +10,8 @@
         }
     ],
     "require": {
-        "php": ">=5.5.0",
-        "maknz/slack": "@dev"
+        "php": ">=5.4.0",
+        "maknz/slack": "~1.0"
     },
     "autoload": {
         "psr-4": {