FEATURE: Require basic ninja-mutex library (arvenil/ninja-mutex)

composer.json

@@ -26,6 +26,7 @@
     "source": "https://git.higidi.com/higidi/ninja-mutex"
   },
   "require": {
-    "php": ">=5.3.0"
+    "php": ">=5.3.0",
+    "arvenil/ninja-mutex": "^0.6"
   }
 }