Replace deprecated minifiers with gulp-cssnano and gulp-htmlmin

gulp-htmlmin currently has to be manually configured; there are no sensible
defaults. These transforms are all relatively safe, and in my experience provide
the bulk of HTML minification gains.

gulpfile.babel.js

@@ -96,7 +96,7 @@ gulp.task('styles', () => {
     .pipe($.autoprefixer(AUTOPREFIXER_BROWSERS))
     .pipe(gulp.dest('.tmp/styles'))
     // Concatenate and minify styles
-    .pipe($.if('*.css', $.minifyCss()))
+    .pipe($.if('*.css', $.cssnano()))
     .pipe($.size({title: 'styles'}))
     .pipe($.sourcemaps.write('./'))
     .pipe(gulp.dest('dist/styles'));
@@ -141,10 +141,20 @@ gulp.task('html', () => {
 
     // Concatenate and minify styles
     // In case you are still using useref build blocks
-    .pipe($.if('*.css', $.minifyCss()))
+    .pipe($.if('*.css', $.cssnano()))
 
     // Minify any HTML
-    .pipe($.if('*.html', $.minifyHtml()))
+    .pipe($.if('*.html', $.htmlmin({
+      removeComments: true,
+      collapseWhitespace: true,
+      collapseBooleanAttributes: true,
+      removeAttributeQuotes: true,
+      removeRedundantAttributes: true,
+      removeEmptyAttributes: true,
+      removeScriptTypeAttributes: true,
+      removeStyleLinkTypeAttributes: true,
+      removeOptionalTags: true
+    })))
     // Output files
     .pipe($.if('*.html', $.size({title: 'html', showFiles: true})))
     .pipe(gulp.dest('dist'));

package.json

@@ -11,12 +11,12 @@
     "gulp-babel": "^6.0.0",
     "gulp-cache": "0.2.2",
     "gulp-concat": "^2.5.2",
+    "gulp-cssnano": "^2.0.0",
     "gulp-eslint": "^1.0.0",
+    "gulp-htmlmin": "^1.3.0",
     "gulp-if": "^2.0.0",
     "gulp-imagemin": "^2.0.0",
     "gulp-load-plugins": "^1.0.0",
-    "gulp-minify-css": "^1.1.6",
-    "gulp-minify-html": "^1.0.4",
     "gulp-newer": "^1.0.0",
     "gulp-sass": "^2.0.0",
     "gulp-size": "^2.0.0",