Revert "Revert "put back PHP 5.5.9 support""

This reverts commit d1752e9.

Author: eugene-matvejev

composer.json

@@ -29,7 +29,7 @@
         "bin-dir": "bin/"
     },
     "require": {
-        "php": ">= 5.6.0 || 7.0.0 - 7.0.4 || >= 7.0.6",
+        "php": ">= 5.5.9 || 7.0.0 - 7.0.4 || >= 7.0.6",
         "leafo/lessphp": "^0.5",
         "leafo/scssphp": "@dev",
         "leafo/scssphp-compass": "@dev"