update node modules

node_modules/clean-css/lib/optimizer/level-1/property-optimizers/background.js

@@ -0,0 +1,23 @@
+var OptimizationLevel = require('../../../options/optimization-level').OptimizationLevel;
+
+var plugin = {
+  level1: {
+    property: function background(_rule, property, options) {
+      var values = property.value;
+
+      if (!options.level[OptimizationLevel.One].optimizeBackground) {
+        return;
+      }
+
+      if (values.length == 1 && values[0][1] == 'none') {
+        values[0][1] = '0 0';
+      }
+
+      if (values.length == 1 && values[0][1] == 'transparent') {
+        values[0][1] = '0 0';
+      }
+    }
+  }
+};
+
+module.exports = plugin;