chore(package): update image-webpack-loader to version 6.0.0

Closes #58

Author: greenkeeper[bot]

package.json

@@ -60,7 +60,7 @@
     "extract-text-webpack-plugin": "^4.0.0-beta.0",
     "file-loader": "^1.1.6",
     "html-webpack-plugin": "^3.1.0",
-    "image-webpack-loader": "^4.0.0",
+    "image-webpack-loader": "^6.0.0",
     "jest": "^22.3.0",
     "morgan": "^1.9.0",
     "nodemon": "^1.14.1",