chore(package): update gulp-htmlmin to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
     "gulp-bower": "0.0.13",
     "gulp-cache": "^1.0.0",
     "gulp-concat": "^2.6.1",
-    "gulp-htmlmin": "^3.0.0",
+    "gulp-htmlmin": "^4.0.0",
     "gulp-imagemin": "^4.0.0",
     "gulp-img-retina": "0.0.4",
     "gulp-rename": "^1.2.2",