Added previous hsl experimental version

Author: Uziel Maximo Luduena

composer.json

@@ -19,6 +19,7 @@
     "hhvm/hhast": "^4.0",
     "hhvm/hhvm-autoload": "^2.0.8|^3.0",
     "hhvm/hacktest": "^2.0",
-    "usox/hackttp": "^0.3"
+    "usox/hackttp": "^0.3",
+    "hhvm/hsl-experimental": "4.37.2"
   }
 }