Update of imagemin dependencies

Author: Eterion

package.json

@@ -17,13 +17,13 @@
     "test": "npm run test:webpack1 && npm run test:webpack2 && npm run test:webpack3 && npm run test:webpack4"
   },
   "dependencies": {
-    "imagemin": "^5.2.2",
-    "imagemin-gifsicle": "^5.1.0",
+    "imagemin": "^5.3.1",
+    "imagemin-gifsicle": "^5.2.0",
     "imagemin-mozjpeg": "^7.0.0",
     "imagemin-optipng": "^5.2.1",
-    "imagemin-pngquant": "^5.0.0",
+    "imagemin-pngquant": "^5.1.0",
     "imagemin-svgo": "^6.0.0",
-    "imagemin-webp": "^4.0.0",
+    "imagemin-webp": "^4.1.0",
     "loader-utils": "^1.1.0",
     "object-assign": "^4.1.1",
     "webpack-cli": "^2.1.3"