bump to clean-css 4.1.5

Author: scniro

package.json

@@ -2,7 +2,7 @@
   "name": "gulp-clean-css",
   "description": "Minify css with clean-css.",
   "homepage": "https://github.com/scniro/gulp-clean-css#readme",
-  "version": "3.4.2",
+  "version": "3.5.0",
   "author": "scniro",
   "license": "MIT",
   "bugs": {
@@ -29,7 +29,7 @@
     "gulpfriendly"
   ],
   "dependencies": {
-    "clean-css": "4.1.4",
+    "clean-css": "4.1.5",
     "gulp-util": "3.0.8",
     "through2": "2.0.3",
     "vinyl-sourcemaps-apply": "0.2.1"