Use csswring and autoprefixer via postcss

csswring supports minification and sourcemaps

package.json

@@ -22,9 +22,10 @@
   },
   "devDependencies": {
     "asset-builder": "0.0.1",
+    "autoprefixer-core": "4.0.1",
+    "csswring": "^2.0.0",
     "del": "^0.1.3",
     "gulp": "^3.8.10",
-    "gulp-autoprefixer": "^2.0.0",
     "gulp-concat": "^2.3.4",
     "gulp-flatten": "0.0.4",
     "gulp-if": "^1.2.5",
@@ -34,6 +35,7 @@
     "gulp-livereload": "^2.1.0",
     "gulp-load-plugins": "^0.7.1",
     "gulp-plumber": "^0.6.3",
+    "gulp-postcss": "^3.0.0",
     "gulp-rename": "^1.2.0",
     "gulp-rev": "^2.0.1",
     "gulp-sass": "^1.1.0",