Process CSS with cssnano in development build

gulpfile.js/tasks/styles.js

@@ -40,7 +40,7 @@ gulp.task('styles:css', function() {
     });
 
     return gulp.src(sources, {base: '.'})
-        .pipe(config.isProduction ? cssnano(cssnanoConfig) : gutil.noop())
+        .pipe(cssnano(cssnanoConfig))
         .pipe(autoprefixer(autoprefixerConfig))
         .pipe(renameSrcToDest())
         .pipe(size({ title: 'Vendor CSS' }))
@@ -66,7 +66,7 @@ gulp.task('styles:sass', function () {
             includePaths: includePaths,
             outputStyle: 'expanded'
         }).on('error', sass.logError))
-        .pipe(config.isProduction ? cssnano(cssnanoConfig) : gutil.noop())
+        .pipe(cssnano(cssnanoConfig))
         .pipe(autoprefixer(autoprefixerConfig))
         .pipe(size({ title: 'Wagtail CSS' }))
         .pipe(config.isProduction ? gutil.noop() : sourcemaps.write())