Use scss for stylesheet.

We can build the scss source to .css and .min.css files with the
`grunt build` command.

package.json

@@ -3,10 +3,12 @@
   "version": "0.5.6",
   "description": "Tiny but perfect jquery scrollbar plugin.",
   "author": "Hyunje Alex Jun <me@noraesae.net>",
-  "contributors": [{
-    "name": "Hyunje Alex Jun",
-    "email": "me@noraesae.net"
-  }],
+  "contributors": [
+    {
+      "name": "Hyunje Alex Jun",
+      "email": "me@noraesae.net"
+    }
+  ],
   "main": "src/perfect-scrollbar.js",
   "repository": {
     "type": "git",
@@ -30,7 +32,9 @@
     "grunt-contrib-csslint": "~0.1.2",
     "grunt-contrib-cssmin": "~0.6.1",
     "grunt-contrib-jshint": "~0.1.1",
-    "grunt-contrib-uglify": "~0.1.1"
+    "grunt-contrib-uglify": "~0.1.1",
+    "grunt-sass": "^0.16.1",
+    "load-grunt-tasks": "^1.0.0"
   },
   "scripts": {
     "test": "grunt travis --verbose"