fix(build): switch to cssnano for CSS optimizations

Replaces the deprecated `grunt-minify-css` with `gulp-cssnano`.

Fixes #9225.

Closes #9236

Author: crisbeto

gulp/tasks/build-scss.js

@@ -10,10 +10,10 @@ var series = require('stream-series');
 var util = require('../util');
 var sassUtils = require('../../scripts/gulp-utils');
 var sass = require('gulp-sass');
-var minifyCss = require('gulp-minify-css');
 var insert = require('gulp-insert');
 var addsrc = require('gulp-add-src');
 var gulpif = require('gulp-if');
+var minifyCss = util.minifyCss;
 var args = util.args;
 var IS_DEV = require('../const').IS_DEV;
 

gulp/util.js

@@ -16,9 +16,9 @@ var uglify = require('gulp-uglify');
 var sass = require('gulp-sass');
 var plumber = require('gulp-plumber');
 var ngAnnotate = require('gulp-ng-annotate');
-var minifyCss = require('gulp-minify-css');
 var insert = require('gulp-insert');
 var gulpif = require('gulp-if');
+var nano = require('gulp-cssnano');
 var constants = require('./const');
 var VERSION = constants.VERSION;
 var BUILD_MODE = constants.BUILD_MODE;
@@ -32,6 +32,7 @@ exports.buildModule = buildModule;
 exports.filterNonCodeFiles = filterNonCodeFiles;
 exports.readModuleArg = readModuleArg;
 exports.themeBuildStream = themeBuildStream;
+exports.minifyCss = minifyCss;
 exports.args = args;
 
 /**
@@ -80,6 +81,15 @@ function autoprefix () {
   ]});
 }
 
+function minifyCss() {
+  return nano({
+    autoprefixer: false,
+    reduceTransforms: false,
+    svgo: false,
+    safe: true
+  });
+}
+
 function buildModule(module, opts) {
   opts = opts || {};
   if ( module.indexOf(".") < 0) {

package.json

@@ -43,12 +43,12 @@
     "gulp-autoprefixer": "^3.1.0",
     "gulp-concat": "^2.2.0",
     "gulp-connect": "^2.2.0",
+    "gulp-cssnano": "^2.1.2",
     "gulp-filter": "^1.0.2",
     "gulp-frep": "^0.1.3",
     "gulp-if": "^1.2.0",
     "gulp-insert": "^0.4.0",
     "gulp-jshint": "^1.5.5",
-    "gulp-minify-css": "^0.3.4",
     "gulp-ng-annotate": "^0.5.2",
     "gulp-ng-html2js": "^0.1.8",
     "gulp-plumber": "^1.0.0",