Update deps. (#71)

Author: gucong3000

package.json

@@ -46,15 +46,15 @@
     "postcss-syntax": ">=0.31.0"
   },
   "devDependencies": {
-    "autoprefixer": "^8.6.4",
+    "autoprefixer": "^9.0.0",
     "chai": "^4.1.2",
-    "codecov": "^3.0.2",
+    "codecov": "^3.0.4",
     "mocha": "^5.2.0",
     "nyc": "^12.0.2",
-    "postcss": "^6.0.23",
+    "postcss": "^7.0.0",
     "postcss-less": "^2.0.0",
-    "postcss-safe-parser": "^3.0.1",
-    "postcss-scss": "^1.0.6",
+    "postcss-safe-parser": "^4.0.1",
+    "postcss-scss": "^2.0.0",
     "postcss-syntax": ">=0.31.0",
     "sugarss": "^1.0.1"
   }