being more explicit with dependencies

Author: dmolsen

composer.json

@@ -26,7 +26,7 @@
 	"require": {
 		"php":              ">=5.3.6",
 		"twig/twig":        "~1.15",
-		"pattern-lab/core": "dev-dev"
+		"pattern-lab/core": "~0.5"
 	},
 	"extra": {
 		"patternlab": {