Swap out glup for files-replace

Fixes:
9 vulnerabilities (2 moderate, 7 high)

package.json

@@ -43,13 +43,14 @@
    "scripts": {
       "step:01": "rimraf build dist **/.DS_Store",
       "step:02": "jshint . --exclude-path .gitignore",
-      "step:05": "gulp minify-css",
-      "step:06": "copy-folder src --ext=.js build",
-      "step:07": "uglifyjs src/hamburger-menu.js --output build/hamburger-menu.min.js",
-      "step:08": "add-dist-header build dist --delimiter=☰",
-      "step:09": "copy-file dist/hamburger-menu.css --folder docs",
-      "step:10": "copy-file dist/hamburger-menu.js --folder docs",
-      "step:11": "html-validator",
+      "step:10": "files-replace src --ext=.css build --concat=hamburger-menu.css",
+      "step:11": "csso build/hamburger-menu.css --output build/hamburger-menu.min.css",
+      "step:12": "copy-folder src --ext=.js build",
+      "step:13": "uglifyjs src/hamburger-menu.js --output build/hamburger-menu.min.js",
+      "step:20": "add-dist-header build dist --delimiter=☰",
+      "step:30": "copy-file dist/hamburger-menu.css --folder docs",
+      "step:31": "copy-file dist/hamburger-menu.js --folder docs",
+      "step:40": "html-validator",
       "pretest": "npm-run-all step:*",
       "test": "mocha spec/*.spec.js",
       "interactive": "npm test && browser-sync docs --watch"
@@ -61,23 +62,15 @@
       "@fortawesome/fontawesome-free": "~6.2",
       "add-dist-header": "~0.3",
       "assert-deep-strict-equal": "~1.0",
-      "babel-minify": "~0.5",
       "browser-sync": "~2.27",
       "copy-file-util": "~0.1",
       "copy-folder-cli": "~0.1",
-      "cssnano": "~5.1",
+      "csso-cli": "~4.0",
       "dna.js": "~2.0",
-      "gulp": "~4.0",
-      "gulp-append-prepend": "~1.0",
-      "gulp-babel": "~8.0",
-      "gulp-postcss": "~9.0",
-      "gulp-rename": "~2.0",
-      "gulp-replace": "~1.1",
-      "gulp-size": "~4.0",
+      "files-replace": "~0.1",
       "jshint": "~2.13",
       "mocha": "~10.0",
       "npm-run-all2": "~6.0",
-      "postcss": "~8.4",
       "rimraf": "~3.0",
       "uglify-js": "~3.17",
       "w3c-html-validator": "~1.1",