[FIX] Switch to maintained fork of "css" package

This solves the issue of having outdated and potential insecure
transitive dependencies.

There are no known behavior changes, so this is considered a
non-breaking change / fix.

See: reworkcss/css#163
See: SamVerschueren/decode-uri-component#6

lib/index.js

@@ -1,7 +1,7 @@
 "use strict";
 
 const path = require("path");
-const css = require("css");
+const css = require("@adobe/css-tools");
 
 
 const diff = require("./diff");

package.json

@@ -82,8 +82,8 @@
 		"url": "git@github.com:SAP/less-openui5.git"
 	},
 	"dependencies": {
+		"@adobe/css-tools": "^4.0.1",
 		"clone": "^2.1.2",
-		"css": "^3.0.0",
 		"mime": "^1.6.0"
 	},
 	"devDependencies": {

test/test-diff.js

@@ -2,7 +2,7 @@
 "use strict";
 
 const assert = require("assert");
-const css = require("css");
+const css = require("@adobe/css-tools");
 const fs = require("fs");
 const path = require("path");