Updates clean-css dependency to version 5.

Author: jakubpawlowicz

package-lock.json

@@ -17,7 +17,7 @@
   },
   "dependencies": {
     "chalk": "^4.1.0",
-    "clean-css": "~4.2.3",
+    "clean-css": "~5.0.1",
     "maxmin": "^3.0.0"
   },
   "devDependencies": {

package.json

@@ -29,15 +29,16 @@ module.exports = function (grunt) {
 
     this.files.forEach(function (file) {
       var options = this.options({
-        rebase: false,
         report: 'min',
         sourceMap: false
       });
 
       var availableFiles = getAvailableFiles(file.src);
       var compiled = '';
 
-      options.rebaseTo = path.dirname(file.dest);
+      if (Boolean(options.rebase)) {
+        options.rebaseTo = path.dirname(file.dest);
+      }
 
       try {
         compiled = new CleanCSS(options).minify(availableFiles);

tasks/cssmin.js

@@ -1 +1 @@
-body{background:url(../test/fixtures/test.jpg)}/*# sourceMappingURL=rebase.css.map */
+body{background:url('../test/fixtures/test.jpg')}/*# sourceMappingURL=rebase.css.map */